Re: Hypothesis testing and magic - episode 2
At 10:23 AM 4/13/00 -0500, Michael Granaas wrote: In addition to defining the variables some areas do a better job of defining and therefore testing their models. The ag example is one where not only the variables are relatively clear so are the models. That is there is one highly plausible reason for rejecting a null that fertilizer does not effect crop production: Fertilizer increases crop production. You have rejected a model of no effect in favor of a model positing an effect. i did not know that ag research ... in this case, production figures ... was so easily accomplished ... it might be relatively easy to distribute fertilizer in different amounts ... over plots ... but even there, there is considerable error ... check out the way our spreaders work on our lawns? and in addition ... every fertilizer i know of is a product that is an amalgamation of several subproducts ... and inert stuff too ... so the distribution of it over plots will not produce identical spreads ... and ... how is production measured? to compare across plots means gathering in crops ... and making some kind of 'volume' measurements ... and that seems much easier said than done now, i would not like to say that doing a fertilizer experiment has the same amount of 'error' as maybe one where we ask if different levels of intelligence impact differentially on problem success in later life ... but these differences are more a matter of degree ... than in one instance it is easy ... and in others it is not maybe we should ask the ag researchers if THEY think doing their research is simple === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
a professor thought that he was producing a test of 50 items at 'about the 50%' difficulty level, that is .. on average, the scores would be about 50%. now, he collected data from a random sample of n=40 of his class ... gave them the test ... and then did a ttest using 25 as the null ... he found (now no fair tossing in other considerations like ... well, this is not planned properly etc just take it on face value the way we ACTUALLY see it in the vast majority of the literature) MTB ttest 25 c1 One-Sample T: C1 Test of mu = 25 vs mu not = 25 Variable N Mean StDev SE Mean C1 40 32.20 9.86 1.56 Variable 95.0% CIT P C1( 29.05, 35.35) 4.62 0.000 - REJECT THE NULL -- -- 0 25 50 where on the number line might there 'real' level of performance be based on the rejected null? another prof looking at the data, and keeping in mind what the professor in the course thought did the following 95% ci ... MTB MTB tint c1 One-Sample T: C1 Variable N Mean StDev SE Mean 95.0% CI C1 40 32.20 9.86 1.56 ( 29.05, 35.35) - CI -- 0 25 50 where are the number line do you think the 'real' level of performance is? now, folks on the list have been trying to argue about what truth is ... or whether we actually could find it ... and i would say that in this case, one might define 'truth' at least two ways: first truth: is the null true? second truth: what is mu? the first truth is of so little value (and only really says, we don't think it is 25) ... but the second gets at the heart of the problem ... what is going on with the students performance ... the first truth and our 'proof' of or NOT of it ... just says WE were good or BAD at formulating the hypothesis ... but does not really get us closer to the second truth ... which speaks directly to the parameter ... === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
hyp test:better def
it appears to me that we are having the same kinds of discussions on this topic as usual and we go round and round ... and where we stop depends on when people get tired of it is progress being made? i wonder ... perhaps some of this time would be better spent defining more what a hypothesis is within the general area of doing research ... FORGET ABOUT STATISTICS FOR A MOMENT ... then, if we agree that there are times ... within the framework of trying to better understand phenomena ... that it is helpful perhaps vital for us to formulate AND test (gather data about) one or more researchable hypotheses then we might get a better handle on 1. what the hypothesis is 2. what is a frameable version(s) of that hypothesis 3. what are some data handling (statistical?) ways of trying to collect and present evidence that will shed some light on how tenable or reasonable it is to keep that hypothesis as a work in progress ... or to decide to abandon it and search for better hypotheses or notions or explanations of phenomena we need to recognize however that 1. truth will not be found by this method ... that is, the absolute truth 2. our efforts at best will move us only closer to better understandings of phenomena .. 3. no matter what we find ... we always have to take it with a huge grain of salt ... finally, i WOULD LIKE to offer some summary points that do seem sensible to me A. the reliance on ... and dominance of ... traditional 'significance' testing ... in almost all of printed scientific literature ... across most disciplines ... is TOTALLY out of whack in terms of what this 'method' can tell us about phenomena B. the failure of statisticians in general, particularly those (me included) who TEACH students about this stuff, to build into their psyches 'priors', in some form, as herman and others have been preaching ... is tantamount to unethical statistical instructional practice and C. if we do A and don't do B ... we do a tremendous disservice to students we work with now, how we reinvent our strategies ... is difficult INdeed ... but, we must try === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: Hypothesis testing and magic - episode 2
At 09:30 AM 4/13/00 +1000, Alan McLean wrote: In the soft sciences it is easy enough to identify a characteristic of interest alan makes good points as usual ... but i totally object to the term 'soft' sciences ... what does soft imply? that the science is bad ... or, that merely that variables are more 'difficult' to measure ... if that is the case, these ought to be called the 'hard' sciences the unpleasant associations with the term 'soft' are uncalled for ... there are excellent 'scientists' (whatEVER that means) in all fields .. and some pretty weak ones too (and gee ... BOTH kinds get tenure!) ... science is science ... and some practice it well ... some don't ... should it be some demerit against them that they happen to have opted for a field of interest ... even if many of the variables are difficult to measure? perhaps that makes it even more challenging ... finally, i would not be so quick to claim that in the areas that are non social science based ... that variables are all the clear and clean cut ... there seems to be tremdous infighting about theories and how to 'validate' them in medicine ... astronomy ... physics ... it is not like everything there is so simple ... maybe don can pop in here with some relevant examples ... i am sure there are 'mean' differences in terms of these things but ... there is a lot more WITHin variation in terms of hardness/softness ... that between disciplines == dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
hyp testing and rho
here are two sample r values ... done in minitab ... and the associated output Correlations: C52, C53 Pearson correlation of C52 and C53 = 0.599 P-Value = 0.000 MTB corr c54 c55 Correlations: C54, C55 Pearson correlation of C54 and C55 = 0.586 P-Value = 0.075 now, minitab prints out a p value for the null hypothesis test of rho =0 ... which for better or worse is fairly standard practice ... from the results of the 'significance' test (and nothing else) ... tell me what this says in terms of what the TRUE rho value might be? === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: examples of excel
i found this ... someone has made some excel demos ... using the lotus product screencam ... which shows desktop work ... http://www.business.utah.edu/~mgtdgw/statmov.htm screencam can be seen at http://www.lotus.com/home.nsf/welcome/screencam you need a screencam player ... which is a plugin you can get at the above At 08:12 AM 4/11/00 -0400, William Dudley wrote: I seem to recall that while back someone posted a listing of URLS for examples of lessons in statistics using MS Excel. I wonder if anyone has that list or can recommend another source. Thanks Bill === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ === === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
At 02:29 PM 4/11/00 -0300, Robert Dawson wrote: The problem is that failure to reject means *either* that the null is true *or* that the sample size too small *or* both; "or" both says then ... that the null IS true AND that sample size is TOO small ... too small for what??? and a classical hypothesis test on its own does not tell you which. -Robert Dawson === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
At 07:12 PM 4/10/00 -0700, David A. Heiser wrote: - Original Message - From: Michael Granaas mailto:[EMAIL PROTECTED][EMAIL PROTECTED] Our current verbal lables leave much to be desired. Depending on who you ask the "null hypothesis" is a) a hypothesis of no effect (nil hypothesis) b) an a priori false hypothesis to be rejected (straw dog hypothesis) c) an a priori plausible hypothesis to be tested and falsified or corroborated (wish I had a term for this usage/real null?) -- The concept of a hypothesis is important. It can be used to teach an important statistical concept. i think that the notion of a RESEARCH hypothesis is helpful ... but, most nulls are not if we spent more time on trying to define a sensible research hypothesis ... and then translate THAT into some working hunch worthy of testing ... rather than defining nulls that in many cases are rather silly ... i would be happier ====== dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
the term 'null' does NOT mean 0 (zero) ... though it is misconstrued that way the term 'null' means a hypothesis that is the straw dog case ... for which we are hoping that sample data will allow us to NULLIFY ... in some cases, the null happens to be 0 ... but in many cases, it does not cases in point: 1. null hypothesis is that the population variance for IQ is 225 2. null hypothesis is that the population mean for IQ is 100 3. to test the variance of a population ... the null is that the chi square value will be degrees of freedom and on and on and on At 10:04 AM 4/10/00 -0500, Michael Granaas wrote: On Fri, 7 Apr 2000, dennis roberts wrote: At 04:00 PM 4/7/00 -0500, Michael Granaas wrote: But whatever form hypothesis testing takes it must first and formost be viewed in the context of the question being asked. this seems to be the key to REinventing ourselves ... make sure the focus is on the question ... AND, to REshape the question FROM what we traditionally do in hyp test ... If you look at Psychology you might well see two traditions, one in which the zero valued null is used in a rather automatic and mindless fashion and another in which researchers work very hard setting up experiments where rejection of the zero valued null does provide some information. set up the null, etc. etc to ... ask the question of real interest ... what effect DOES this new treatment have? what kind of correlation IS there between X and Y? In the second tradition I spoke of you find people asking exactly these types of questions once they have established that their experimental results are not due to chance. They use the hypothesis test as a step on the road to understanding, not as an end in and of itself. To me this second group acts more like model fitters (emphasis on prediction) than they do like hypothesis testers (emphasis on rejecting nil effects). Even though this second group rejects some nil valued hypothesis they, unlike the first, ask questions about things like effect size or functional form of an effect rather than simply declaring the effect is not zero and drawing some final conclusion. For myself I try to get students at all levels asking the types of questions that Dennis suggests as being obvious follow-ups to rejecting some nil hypothesis. I cannot claim a great deal of success, but I am trying. what IS the difference between the smartness of democrats and republicans? if you ask questions that way ... they do not naturally or sensibly lead to our testing the typical null hypotheses we set up Yes. There are a variety of answers to this problem, but, rejecting the no difference hypothesis when it is a priori false is not among them. Michael *** Michael M. Granaas Associate Professor[EMAIL PROTECTED] Department of Psychology University of South Dakota Phone: (605) 677-5295 Vermillion, SD 57069 FAX: (605) 677-6604 *** All views expressed are those of the author and do not necessarily reflect those of the University of South Dakota, or the South Dakota Board of Regents. === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
At 01:16 PM 4/10/00 -0300, Robert Dawson wrote: No if you have to start "a more sensible null would be perhaps" you almost surely do not have a hypothesis worth testing. now we get to the crux of the matter ... WHY do we need a null ... or any hypothesis ... (credible and/or sensible) to test??? what is the scientific need for this? what is the rationale within statistical exploration for this? i am not suggesting that we don't need or must not deal with inferences from sample data to what parameters might be ... but, i fail to see WHY that necessarily means that one has to have a null hypothesis of any kind perhaps this is what needs to be debated more ... what function does having a hypothesis really have? if any ... it would be useful if we could have some short listing of reasons why and, some examples where WITHOUT a hypothesis, we are unable to make any scientific progress === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
At 01:16 PM 4/10/00 -0300, Robert Dawson wrote: both leave the listener wondering "why 0.5?" If the only answer is "well, it was a round number close enough to x bar [or "to my guesstimate before the experiment"] not to seem silly, but far enough away that I thought I could reject it." then the test is pointless. -Robert Dawson YOU HAVE made my case perfectly! ... this is why the notion of hypothesis testing is outmoded, no longer useful ... not worth the time we put into teaching it ... in the case above ... i would ask: what is the population rho value ... THAT is the important inferential issue ... there is no reason why we would have to say: i wonder if it is .5 ... let's TEST that, or ... i wonder if it is .7 ... let's TEST that ... we can simply ask the question and try to get an answer to that ... and there is no need to test a pre formulated null to get some sensible answer to the question no need for ANY null ... therefore no need for any hypothesis test if 0 is absurd ... and, if i hypothesized .5 and you ask why .5??? then we could have asked anywhere from 0 to .5 ... and they would have been just as non functional ... that's it ... hypothesis testing is non functional === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
scientific method
here are a few (fastly found i admit) urls about scientific method ... some are quite interesting http://dharma-haven.org/science/myth-of-scientific-method.htm#Overview http://teacher.nsrl.rochester.edu/phy_labs/AppendixE/AppendixE.html http://idt.net/~nelsonb/bridgman.html http://www.brint.com/papers/science.htm http://koning.ecsu.ctstateu.edu/Plants_Human/scimeth.html http://ldolphin.org/SciMeth2.html http://www.wsu.edu:8080/~meinert/SH.html http://www.phys.tcu.edu/~dingram/edu/pine.html now, i know there are tons more ... and, i offer no guarantees about the above ... === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
the logic behind the null hypothesis method is flawed ... IF you are looking for truth AND you keep following the logic of testing AGAINST a null ... first, say you reject the null of rho = 0 ... then, LOGICALLY ... this says that since we don't know what truth is ... just what we think it isn't ... we go second, make the null as rho = .05 ... then .1, then .15 ... on and on UNTIL we reach that magical spot (if ever) ... when we had the null of rho = .65 ... and we suddenly RETAINED the null! i guess we know what the truth is now, or, do we? At 05:20 PM 4/10/00 -0400, Rich Ulrich wrote: Just because Dennis has trouble with the null hypothesis, that does not mean that it is a bad idea to use them. maybe not ... but i don't see that many if any reasons why and the discussions are not swaying me ... (of course, that is not the posters faults ... maybe just mine) === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
hyp testing
let's say that today ... we as the statistical community decided, by democratic vote, that the concept of 'hypothesis testing' ... which has essentially dominated statistical work for as long as i can remember (which, er um ... is a LOT of years!) ... is relegated to the 'we USED to do this stuff' category just THINK about this what would the vast majority of folks who either do inferential work and/or teach it ... DO what analyses would they be doing? what would they be teaching? === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: comparing variances
the discussion of comparing variances brings to mind the following ... and is related to the post i just sent re: hyp testing let's assume that we are interested whether there is some difference in treatment effects ... as measured by means ... our null is the mu1 = mu2 now, we use the 'standard' t test ... and forgive me, pooled variances ... where the assumption is that this is a test of MEANS ... not differences in variances ... so we assume equal variances. but, given the data ... we suspect that there might be a difference in variances so ... we do the (not preferred method as has been mentioned a few times) classic F test ... first s square on top divided by second s square on the bottom HOWEVER ... as has been pointed out ... this test assumes for proper interpretation that the populations are normally distributed ... SOO ... given simple dotplots of the samples of data ... we think that there could be some non normality going on here ... S ... we look for a test of normality ... and of course, when we find one, there will be assumptions for IT too thus, what we are really interested is the difference in population means ... BUT, before we can look at this ... we have to check the equal variance assumption ... BUT ... before we can look at this we ... need to check on the normality assumption of IT sort of a vicious circle again ... if we had decided to abandon the notion of hypothesis testing ... ALL of this flies out the window!!! (is that windows 95??? or 98??? or 2000??? or ...WINNT???) === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
i was not suggesting taking away from our arsenal of tricks ... but, since i was one of those old guys too ... i am wondering if we were mostly lead astray ...? the more i work with statistical methods, the less i see any meaningful (at the level of dominance that we see it) applications of hypothesis testing ... here is a typical problem ... and we teach students this! 1. we design a new treatment 2. we do an experiment 3. our null hypothesis is that both 'methods', new and old, produce the same results 4. we WANT to reject the null (especially if OUR method is better!) 5. we DO a two sample t test (our t was 2.98 with 60 df) and reject the null ... and in our favor! 6. what has this told us? if this is ALL you do ... what it has told you AT BEST is that ... the methods probably are not the same ... but, is that the question of interest to us? no ... the real question is: how much difference is there in the two methods? our t test does NOT say anything about that 1 to 6 can be applied to all sorts of hyp tests ... and most lead us essentially into a dead end At 04:23 PM 4/7/00 +, j. williams wrote: Some of us in the minority would not follow what might be "fashionable." I am one of those who believe hypothesis testing is still an important and integral part of statistics. Hypothesis testing is but one tool in the whole arsenal however. OTH, I'm an old guy who went through graduate school way back in the 60s. Teaching old dogs new tricks is not easy, right? If such a vote were taken today with the results suggested by Mr.Roberts, I know I have successfully misled literally thousands of students. Would re-education be the answer? [EMAIL PROTECTED] (dennis roberts) wrote in [EMAIL PROTECTED]: let's say that today ... we as the statistical community decided, by democratic vote, that the concept of 'hypothesis testing' ... which has essentially dominated statistical work for as long as i can remember (which, er um ... is a LOT of years!) ... is relegated to the 'we USED to do this stuff' category just THINK about this what would the vast majority of folks who either do inferential work and/or teach it ... DO what analyses would they be doing? what would they be teaching? === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ === === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: hyp testing
At 04:00 PM 4/7/00 -0500, Michael Granaas wrote: But whatever form hypothesis testing takes it must first and formost be viewed in the context of the question being asked. this seems to be the key to REinventing ourselves ... make sure the focus is on the question ... AND, to REshape the question FROM what we traditionally do in hyp test ... set up the null, etc. etc to ... ask the question of real interest ... what effect DOES this new treatment have? what kind of correlation IS there between X and Y? what IS the difference between the smartness of democrats and republicans? if you ask questions that way ... they do not naturally or sensibly lead to our testing the typical null hypotheses we set up === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
norm pdf
how come when you do a pdf on a unit norm distribution and one say, where mean is 100 and sd = 15 ... you get different pdf values along the Y axis??? is it just because the lenght of the continuity along X is narrower/wider? 0.030+ - C2 - * * * - -* * 0.020+ - - * * - - 0.010+ * * - - ** - * * -* * 0.000+* * * * * * +-+-+-+-+C1 6080 100 120 140 MTB plot c4 c3 Plot - 0.45+ - C4 - * * - * - * 0.30+ * - - * * - -* 0.15+ * - * - * -** - * * 0.00+* * * * +-+-+-+-+C3 -2.4 -1.2 0.0 1.2 2.4 MTB === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: Texts: Factor Analysis
go to http://www.sagepub.com/ search on ... factor analysis ... some nice short books here At 03:06 PM 4/5/00 +0200, Gottfried Helms wrote: [EMAIL PROTECTED] wrote: What are your favorite book(s) on factor analysis? What do you think of R. Gorsuch's book? My favorite is Stan Mulaik "The foundations of factor analysis". It is comprehensive and still straightforward from the introduction to all covered themes. I have tried different others, but none was like that. Not being educated mathematician I felt I got most that I needed with a good insight of the principles. One similar is from Dirk Revenstorf, but I doubt it is available in english. Gottfried Helms. -- - Gottfried Helms Soz.Päd./Soz.Arb. FB04 // FG Prevention Rehabilitation at University D-34109 Kassel Moenchebergstr. 19 B email: mailto:[EMAIL PROTECTED] www: http://www.uni-kassel.de/~helms === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ === === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: Calculator policy
the other thing i wanted to mention was that ... if you develop some strict calculator policy ... then you spend too much time at the beginning of a class ... checking to make sure that each student ONLY has what is allowed ... in addition, since good calculators allow storage ... and we would encourage students to have this kind ... then when it comes to a test ... you either have to SUPPLY any one who wants one with one ... OR, you are putting at some disadvantage those with real goods ones ... that they can't bring ... compared to students who have simpler ones ... and CAN bring them if you are that worried about what they can or can't do with the calculator ... don't allow ANY calculator ... other than their HEAD ... to be used. we have an analogous situation for our doctoral students who take "written" comprehensives ... some would like to use the computer for word processing ... then we are all bent out of shape worrying about what they might bring in ON a disk or, if we allow them to use their OWN laptops ... what MIGHT they have HIDDEN inside ... ??? this is too much worry that a well constructed test ... would keep us from. === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
do we need huge sample sizes?
the purpose and any inferential statistical procedure is to either answer the question: what is the parameter, or ... to test some specific hypothesis ABOUT a parameter ... thus, the goal of inferential statistics IS finding the parameter. now, significance is nothing more than asking what is the p value for getting some STATISTIC IF the parameter had been some value ... so, in essence, significance testing is about finding the parameter larger sample sizes (random i hope) get us closer to the answer we want ... what is the parameter or ... what is it NOT in this context, you can't have a sample that is too large since, it will systematically get you closer and closer to the truth ... which is what are goal is ... the title of this post should not be ... Sample size: way too big ... but, sample size ... do we need a HUGE sample size in all cases to answer the question that we have about the parameter ... in that context, the answer is clearly no At 11:01 AM 03/22/2000 +, P.G.Hamer wrote: DeLa wrote: I have been trying to explain to some co-workers that a sample can be too big. That is not very easy because it is contratictory to what intuition says. Can someone point me to some good arguments or literature? Or correct me if my assumption is wrong? I can see that huge sample might create problems by making some sorts of analysis too computationally demanding. A large sample will also expose the absurdity of some tests of significance. Can you explain your thinking? Peter === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ === === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: over and above
At 08:19 AM 03/21/2000 -0500, Herman Rubin wrote: The purpose of any course should be the development of knowledge and the ability to use it. Even the use of assignments for any other purpose does not contribute to education. Assignments for the purpose of having the students do assignments, or even for the purpose of grading beyond the minimum necessary, are very common and in my opinion helping to lower the quality of education. It a student already knows how to do it, that student should not have to do it. It becomes busy work. this sounds great ... but, how does the instructor KNOW this if not through some form of work that you have students engage in and let the instructor look at? not admitting that the projects i give to students amount to busy work (i am sure many students would claim that) ... but, much of education and by that i mean LEARNING ... IS busy work ... busy to the extent that you practice something sufficiently so that it becomes 'natural' to you ... to think that way, to write that way, to solve problems that way ... etc. === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
over and above
grading projects for a first assignment REreminds me that ... some students go way above and beyond the call of duty when doing projects ... in my case, they have to download a file ... do some analyses ... and then do some write up of what they found. now, some go to alot to trouble to do very nice documents in a word processor and have gone to fancy extents ... whereas others will use (minitab is the package in this case) minitab ... and do all their work in it (which is possible) and turn in an acceptable document ... say the right things, etc. the QUALITY of the document is not a gradable criterion (in my system ... maybe it should be) ... but, how do any of you deal with this sort of thing ... whether it be a document to be turned in or some other assignment ... some just go WAY over what is required ... of course, penn state has no A+ grade category .. !!! === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: Power for Pilot Studies
well, this is interesting indeed ... for let's say that you did adopt a .1 level for a pilot AND, you just happened to reject the null IN the pilot ... is THAT sufficient justification for committing more time and resources TO a large main study?? the implication from this pilot result is that ... this means that the trend would continue in a more dramatic or noticeable way IN a main study ... and you have no justification for that based on the p value you have adopted in your pilot study ... or, think about it this way ... what IF your p value had been .001 based on your pilot data ... why do any more? well, there are lots of reasons ... the importance of the p value is so minimal even in the best of circumstances ... to use it THIS way is even worse. the main thing you should be doing in a pilot study ... is to first ... iron out the bugs of the methods and procedures ... after all, someone should have already approved of the 'idea' ... and here is a chance to get your ducks in a row with protocols, instrumentation, times for doing things, etc. the second main purpose would be to see if there is ANY evidence at all in the generally predicted direction ... FORget the application of the fancy inferential tests and worrying about alpha ... or power at this stage ... At 01:21 PM 03/15/2000 -0800, Andy Avins wrote: We proposed a pilot clinical trial that was shot down by a local review committee. are you saying that it was shot down BECAUSE you proposed to use a pilot alpha of .25??? this is hard to believe ... but, it could be true ... if it were and that were the ONLY problem ... is this not SO simple to fix??? just change it to .1! i would suspect that there are other more important issues that were considered ... but since we are not privy to these ... it is difficult to comment here Lacking any other guidance, we arbitrarily chose an alpha of 0.25 for doing the power calculations (reasoning that we didn't want to set too stringent a standard for rejecting the null and not proceeding with a more definitive trial). We were criticized for not adopting a more conventional standard of alpha=0.10. I've never heard that there was any convention for this sort of calculation. the basic idea is ... in a pilot ... don't make it AS hard to reject the null as in a full blown study ... but, the use of .1 as THE value for a pilot is just as arbitrary as it is to say that we will use .05 or .01 for the MAIN study ... focusing on alpha is only half the deal ... there is a type II error too that could be FAR more critical in a given setting than alpha ... WHEN WILL WE GET OVER OUR FIXATION ON ALPHA!!! Does anyone have any thoughts or references for sample size calculations for pilot studies? Thanks much in advance! --Andy --Andy Avins, MD, MPH Assistant Professor Department of Medicine Department of Epidemiology Biostatistics University of California, San Francisco E-mail: [EMAIL PROTECTED] Tel: 415-597-9196 === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ === === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
mode
i use minitab and it does not display anywhere the mode (not saying it should) ... does anyone who uses any other software know if your software displays mode/modes in any command or output display? (i don't mean a frequency distribution where YOU can locate it ... but, rather ... it lists AS the mode/modes ... values) === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
grouped dist
in minitab ... is there a way to make a grouped frequency distribution and store the results? for example ... C1 Count 10 1 12 2 14 1 15 1 16 2 19 1 20 1 21 1 22 2 23 2 24 1 27 1 29 3 30 1 N= 20 now, in the oldtime graphics (which mtb calls 'obsolete') ... i can do a hist my making the lowest interval have a midpoint of 12 ... and with increments of 5 for the interval size ... but, this is just display output ... other than doing weird cutting and pasting ... can the midpoint values be stored along with the tally of the frequency IN those intervals? MTB hist c1; SUBC start 12; SUBC incr 5. Histogram Histogram of C1 N = 20 MidpointCount 12.004 17.004 22.007 *** 27.004 32.001 * === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
Re: Internet Email sampling
a lot of this depends on who the target audience is is it adults in general? those who have interest in computers? those who 'do' email? those who are on email lists? this is your first concern then, after deciding on the above ... one has to assess IF a sampling plan will get TO those folks in some representative way ... using the internet? for example ... what if you really were interested in a target audience of email users ... and users of lists in particular ... which lists do you survey on? how do you get access to these? and ... we all know of course that on lists ... you have active participants and lurkers ... how do you get representativeness from each of these subgroups? what seems like a simple notion is very complicated At 04:11 PM 02/28/2000 +0200, Grant wrote: Hi all, We have been approached over the last week or so to conduct a number of internet and e-mail surveys. One common theme is the issue of sampling. Can anybody point me to any sites that gives a sound discussion of the disadvantages of 'self selection' or any other sampling issues. Any discussion on this group will also be valued. Regards, Grant === This list is open to everyone. Occasionally, less thoughtful people send inappropriate messages. Please DO NOT COMPLAIN TO THE POSTMASTER about these messages because the postmaster has no way of controlling them, and excessive complaints will result in termination of the list. For information about this list, including information about the problem of inappropriate messages and information about how to unsubscribe, please see the web page at http://jse.stat.ncsu.edu/ ===
introstat-l (long)
This post is rather long, sorry. I have started a new listserv ... called INTROSTAT-L ... that will be housed here at Penn State, and uses the list server lists.psu.edu. Here is a brief explanation of what the purpose of the list is, and information about who the list has been primarily designed for. You might want to have a look at my initial description of the nature of this list below. But, here is a way you can join the list. Send an email message in THIS format: TO: [EMAIL PROTECTED] You don't have to do anything else. Let me know if you have problems. It seems to me that a valuable service of a list would be to be structured approximately like a COURSE in statistics, and that is what is behind the creation of INTROSTAT-L. INTROSTAT-L will present and sequence material that is commonly presented in a general purpose (perhaps more social science oriented) introductory course in statistics. Most of the topics will be rather traditional and will include things like: Organization of data/ Averages/ Variability/ Measures of location Scatterplots and correlation/ Simple reqression/ Sampling from populations Sampling error of means/ Inferences about means/ Inferences about frequency data/ Errors in hyp testing and basic notion of power Now, we can debate until we are blue in the face whether this is the right 'set' of content or not. I don't want to get into that debate. The basic strategy will be to offer, from this end, some introductory material about a topic, and then welcome other input from subscribers about that topic. At the moment, I am working with 1 or 2 others to be more regular contributors who will add observations and examples, as follow ups to my initial posting. Then, the list in general is welcomed to chime in. After a topic has more or less 'run its course', I will start an introduction to the next topic and we will move on. Here are a few notes about this process: 1. This will NOT be a list (like EDSTAT for example) where it is commonplace to POSE questions. The list is not a question and answer source. Rather, the main purpose is to present sequenced discussion about intro stat course topics. 2. The list will stress the ARCHIVING function as a means for subscribers to gather information about previous topics. 3. This is deliberately a low tech operation ... in that, the vast majority of the discussion will be in TEXT form on the list. Now and then, as is warranted by the content, I MAY place some material on my website ... for example, it is rather difficult to show a regression LINE on screen in a text file. 4. For SURE, from time to time, web links will be mentioned for people to consider visiting. 5. I will use Minitab as the software for showing simple examples. Again, I will do it in such a way as to be able to include my output on the email screen ... and not rely on fancier versions of graphs, etc. Who Can Join: Anyone can join but, you MUST join the list. I am particularly interested in having STUDENTS (perhaps graduate students mainly) join who are in courses related to introductory statistics. Students are welcomed! And, they can contribute IF they have something to add to our general postings about a topic. However, again ... this is NOT a list where we accept basic questions being posed, about a disparate and unconnected set of topics. Please pass along this message to other colleagues who might be interested and also to students (announce in classes if you want) you know who might find it valuable to look in and/or might like to participate in such a list. Also, you may REpost to other lists if you think appropriate. If you have ANY questions about the list, please don't hesitate to send me a note. I am sure that this will be an evolving enterprise and, all will not be perfect. But, hopefully we will learn and revise, and the goal is to make the list a useful one for those interested in learning about introductory statistics, or wanting to refresh ones self or for those who might want to contribute to the discussions about various topics. === This list is open to everyone. Occasionally, people lacking respect for other members of the list send messages that are inappropriate or unrelated to the list's discussion topics. Please just delete the offensive email. For information concerning the list, please see the following web page: http://jse.stat.ncsu.edu/ ===
Re: ANOVA causal direction
At 12:40 PM 2/10/00 +, sofyan2000 wrote: Is there a statistical test in ANOVA / MANOVA that can show the causal direction between 2 variables (Independent and Dependent). i don't think so ... this is determined (if it can be at all) by the DESIGN of the investigation ... and what you did when you called a variable INDependent and DEpendent ... for example ... say i experimentally vary the amount of time i allow students to study for a test AND, on followup ... i find that the means on the test vary positively with the amount of time i maniupated ... it seems to me that the DESIGN says (if it can say anything) that time produces test performance . surely the other way around would make no sense what kind of data are you thinking about when you pose this question? == dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm === This list is open to everyone. Occasionally, people lacking respect for other members of the list send messages that are inappropriate or unrelated to the list's discussion topics. Please just delete the offensive email. For information concerning the list, please see the following web page: http://jse.stat.ncsu.edu/ ===
Re: Statistics Software
FIRST you might want to have a look at clay helberg's great page ... and follow the link on the left to Software .. http://www.execpc.com/~helberg/statframes.html there are many packages that will easily do what you want ... minitab is one ... you can download a free full version for 30 days as a trial ... at ... http://www.minitab.com you might also want to follow the link below to many online stat routines ... where you can do analysis online ... maybe you can find what you need http://members.aol.com/johnp71/javastat.html At 10:22 AM 2/10/00 -0500, Shana Mueller wrote: Hi, I am looking for a stastical software package I have only used the JMP software (mostly for Design of Experiments) in the past but am looking for software that will not only help in planning experiments, but also one in which I can input my data from Excel, do regression analysis and be able to get presentation worthy graphs. As I recall, JMP did not have a good graphing program. Thanks! Shana Mueller [EMAIL PROTECTED] === This list is open to everyone. Occasionally, people lacking respect for other members of the list send messages that are inappropriate or unrelated to the list's discussion topics. Please just delete the offensive email. For information concerning the list, please see the following web page: http://jse.stat.ncsu.edu/ === == dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm === This list is open to everyone. Occasionally, people lacking respect for other members of the list send messages that are inappropriate or unrelated to the list's discussion topics. Please just delete the offensive email. For information concerning the list, please see the following web page: http://jse.stat.ncsu.edu/ ===
search engines
it appears that the longer i go, the more info i tend to gather for other folks ... especially via the web. now, i have my favorite search engines ... and for sure, none is perfect. in addition to things like altavista, infoseek, etc. ... i like ones such as google, directhit, dogpile, and alltheweb ... are there any that YOU have found to be particularly useful in your searches? i know that it helps to be able to narrow this down but ... the information i gather could be about almost anything ... suggestions are most welcome ... thanks! -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
Re: y2k confound
At 08:20 AM 1/7/00 -0500, Paige Miller wrote: I read somewhere that a state government agency deliberately left three computers unfixed for Y2K and they crashed immediately and were useless. the problem with this is how does one know that these 3 would not have crashed even if there were 'fixes' done ... they could have been old clunkers that were on the verge of going anyway ... now, if the department had say 50 machines ... and split them in 1/2 at random ... and "fixed" one half and did not fix the other half ... with a large difference being observed ... we might make something of that ... the inherent problem we have in this situation is that ... there is essentially NO pre measure of 'incidents' of problems to compare the post to ... all we really have is the assumption that there would be hell to pay IF we did nothing (which MAY have been true but the design and available info makes it tough to prove that ...) -- Paige Miller Eastman Kodak Company [EMAIL PROTECTED] "It's nothing until I call it!" -- Bill Klem, NL Umpire -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
y2k confound
happy new year to everyone ... hope your y2k +1 year is great! now, the y2k scare provides us with an excellent example of confounds (more or less) .. consider the following: Time One: lots of hype about "potential" disasters related to y2k ... (PRETEST) Time Two: billions of $$$ spent on "fixing" y2k "problems" (TREATMENT) Time Three: world notes relatively few y2k problems ... (POSTTEST) so ... did the "treatment" lead to the observation of "few problems"? -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
Re: transcript
if i saw two transcripts ... one where someone has on paper, having taken an intro stat course say with a grade of B ... and another one where there is NO mention of ever having taken ANY stat i think it would be fair to assume that the first knows something about statistics or at least has been exposed to some ideas and the p value about this for the other person is INdeterminant ... now, from an information point of view ... that provides some information that differentiates between the two ... IF that kind of information is important to the one reading the transcript ... i know that herman would agree (though i have not asked him) that all of this only gives us some information that helps us offer some probability statements as to how "nature" exists or the various "states of nature" ... at least herman talks about this over and over again ... and, in this context a transcript merely gives us some more information about certain states of nature ... in this context ... transcripts are helpful ... ========== dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm
Re: grading on the curve
it is one thing to try to accurately assess and indicate what someone knows or can do, this is not too difficult to accomplish ... but it is quite another thing to give a grade .. which is a VALUE judgement as to the "worth" of a performance ... while we have decent tools to indicate the former, it is apparent that society still has not quite figured out about WHAT the latter should represent ... level of capability? current performance? effort? potential? mixture? this is why grading is sort of a crap shoot ... since there really are NO clear rules and definitions ... then this translates into unclear procedures for doing so in real practice ... and, college catalogs don't help ... have a look at where grades are discussed and see if that helps much i doubt it ====== dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm
Re: adjusting marks; W. Edwards Deming
this shows how naive deming really was ... who says learning "should" be a joy? learning is WORK ... and, work is hard. now, some kids really relish the task and challenges ... but many others do not ... should we blame THEM? but, i don't really see what deming has to do with our discussion of "adjusting" marks ... At 08:33 AM 12/22/99 -0600, Peter Westfall wrote about deming: The motivation for the students should be in Joy of Learning (one of Deming's 14 points) rather than the grade. -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
grading on the curve
this discussion is interesting ... there seems to be TWO general kinds of "grading" on the curve ... it would be interesting to try to "estimate" how frequently each happens ... 1. LOWERing cutoffs ... thus, INcreasing the #s of those getting various higher grades 2. making cutoffs such that the distribution of GRADES resembles a normal distribution i assume that #1 occurs much more frequently and, from my perspective, there is NO good rationale for doing #2 ... unless one assumes that ability within a class is normally distributed AND ... and far more crucial ... that achievement SHOULD resemble the distribution of ability ... in any case ... instructors are suppose to give students some reasonable description of the grading system used ... at the BEginning of a course ... which i assume would include some facimile of a grading scale ... or what one has to do to earn certain grades ... and in this context, i would think that anyone who might 'consider" RAISING cutoffs so that FEWER students get higher grades ... would be challenged from students .. as this appears to border on unethical practice ... At 02:32 PM 12/22/99 -0500, [EMAIL PROTECTED] wrote: I never, as a teacher, used any curving procedure to lower students grades! ========== dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm
Re: adjusting marks
first, why does she want to do this? second, does the distribution as is, look like a normal distribution? if not ... why would you want to FORCE it to look like that? third ... usually, "curving" means lowering the cutoffs ... that were established at the beginning of a course (maybe in the syllabus) if that is the case ... then there is NO statistical rationale for this ... simply, your "gut" feeling that not enough students are making As, Bs, etc ... SO, you move the cutoffs down until YOU feel comfortable ... At 04:23 AM 12/21/99 +, Generic wrote: My wife wants to adjust marks for a course she is marking. Does someone have a formula or something for using a bell curve to move them up or down? I have done this sort of thing about 15 years ago, but I can't remember any of it! -- -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
Re: adjusting marks
At 02:34 PM 12/21/99 -0600, EAKIN MARK E wrote: Dennis Roberts writes: i said this ... third ... usually, "curving" means lowering the cutoffs ... that were established at the beginning of a course (maybe in the syllabus) if that is the case ... then there is NO statistical rationale for this ... simply, your "gut" feeling that not enough students are making As, Bs, etc ... SO, you move the cutoffs down until YOU feel comfortable ... and mark countered In the case of my teaching philosoply, I will have to disagree with the above. To me, a student's grade can be expressed as but, i counter counter with ... sorry ... grading is PRIMARILY a subjective activity ... there is no other way to put it. now, you can have test scores, project scores, other observations, speeches, homework, knowledge from previous classes, etc. ... you name it. but, in the final analysis ... you put all this stuff together ... and then you DECIDE where to put the cut points ... and, if anyone out there thinks the placing of cut points in typical classes in schools is objective ... then merry christmas to you and to all a good night! ========== dennis roberts, penn state university educational psychology, 8148632401 http://roberts.ed.psu.edu/users/droberts/droberts.htm
z and t
of course ... if one believes that NEITHER really give you any useful information about population parameters ... means ... or correlation values, etc. ... remember, the t distribution and associated tests using it, is not JUST used for means ... THEN, maybe this distinction is trivial ... in all cases ... and the effort needed (and it does take SOME effort) to make this distinction is not worth the instructional time devoted to it but of course, this is just one view in cyberspace ... (and my eudora keeps telling me that "cyberspace" is a misspelling it needs to get with the program!) -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
Re: GLM vs. ANOVA
in minitab for example ... the command ANOVA insists on equal ns in the cells ... glm does not ... this is not a conceptual difference as don was pointing out ... but, it is important IF you happen to be using minitab -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
RE: teaching statistical methods by rules?
i would highly recommend a paper by ken brewer ... titled: behavioral statistics textbooks: source of myths and misconceptions, Journal of Educational Statistics .. Fall, 1985, V 10, #3, pp 252-268 ... for an excellent discussion of the CLT At 12:20 PM 12/15/99 -0600, Olsen, Chris wrote: Hello Robert and All -- It would seem to me that more than this most can be said. If my reading of the central limit theorem is up to snuff, I should be able to use the "Z test with s" without an underlying assumption of the normality of the parent population, required for the t. I am not etching n = 30 in stone, here -- but there is _some_ large n that will make the underlying sampling distribution of the mean sufficiently close to normal to justify the "Z with s." -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
Re: Rank, Awful
At 11:37 PM 11/29/99 -0500, Bob Hayden wrote: Someone found another bug in Excel's statistics routines. Someone else came up with a clever alternative. What you have to think about is all the bugs you have not noticed yet. Anybody can do statistic with Minitab, but you need a Ph.D. in statistics to (safely) do statistics with Excel. The LAST people in the world who should be using Excel for statistics are beginners. of course, on the OTHER side of the coin ... the procedure for RANK in minitab (for example) either ranks things correctly or bassackwards (that is ... RANK AWFUL) since big numbers have big ranks assigned ... now, if you are ranking average golf strokes per round over the year for pro golfers, that is good but, if you are ranking high school cumulative gpas for seniors, that is not. thus, EVEN in stat packages, one needs to UNDERSTAND what one is doing inorder to use the package correctly ... most packages give tons of output but, without the proper INput understanding, it is just output. -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
Re: Fw: Rank Awful
i would like to comment on this ... without getting anyone mad at me. i have heard this argument many times before but ... i think that if we promulgate this ... what it means is that we are not doing our students any favors ... i don't view some general stat package as a "specialist" package ... it is how people who do statistics work, work. it is comparable to saying that since everyone might have notepad on their machine, that that is the way they should do word processing. we need to alert students to general tools that are DESIGNED to do certain things ... and, if they become professionals in the field .. then they should know that sometimes you need to purchase "tools" for your work sure, excel can do (with its plugin modules) much of this stuff but, A) the algorithms for doing much of this are not very efficient nor, is their accuracy without conern, and B) excel is limited in many ways so, for many things one has to go to the REAL things anyway ... why don't start them on that path in the first place? software is cheap nowadays ... for example ... one can go to http://www.e-academy.com ... and download minitab) as one exmaple ... for $25 for 6 months ... or go to http://www.minitab.com ... and get it totally free for 30 days ... or buy good student editions of packagages for, reasonable prices OR, there are shareware packages that are pretty good ... and even online routines (like statlets) ... in this climate ... it seems even LESS of an argument that students might not have access to real packages .. they are all over the place and cheap. but, this is just my opinion ... At 06:46 PM 11/29/99 +, Graham D Smith wrote: I guess "nice" is in the eye of the beholder. I view this as another good reason NOT to use Excel for Statistics! Please use the right tool for the job. Jon Cryer Sometimes the right tool for the job is Excel. Most of my students will not have access to specialist statistical software after they graduate. Although Excel has many shortcomings, it is widely-available. Dr Graham D. Smith Psychology Division School of Behavioural Studies University College Northampton Boughton Green Road Northampton NN2 7AL Tel (01604) 735500 Ext 2393 Email [EMAIL PROTECTED] - Original Message - From: Jon Cryer [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, November 29, 1999 5:54 PM Subject: Re: Rank Awful I guess "nice" is in the eye of the beholder. I view this as another good reason NOT to use Excel for Statistics! Please use the right tool for the job. Jon Cryer At 05:58 PM 11/26/99 +0100, you wrote: Very nice solution. It can be reduced even to the last part: RANK(A1,A$1:A$6,1)+(COUNTIF(A$1:A$6,A1)-1)/2) Ivan You can modify the rank() function using the following one: IF(COUNTIF(A$1:A$6,A1)=1, RANK(A1,A$1:A$6,1), RANK(A1,A$1:A$6,1)+(COUNTIF(A$1:A$6,A1)-1)/2) In this setting, the data range is A1:A6 (as the example you mentioned in your email), and ranking is in the ascending order, e.g. smaller number gets smaller rank. You can type this function in cell B1, and copy the formula to B1:B6. Let me know if you need further info. Jay Ivan Zezula, Safarik University, Kosice _ - | \ Jon Cryer[EMAIL PROTECTED] ( ) Department of Statistics http://www.stat.uiowa.edu\ \_ University and Actuarial Science office 319-335-0819 \ * \ of Iowa The University of Iowa dept. 319-335-0706\ / Hawkeyes Iowa City, IA 52242FAX319-335-3017 | ) - V -- 208 Cedar Bldg., University Park, PA 16802 AC 814-863-2401Email mailto:[EMAIL PROTECTED] WWW: http://roberts.ed.psu.edu/users/droberts/drober~1.htm FAX: AC 814-863-1002
