Re: Normality in Factor Analysis
Robert Ehrlich [EMAIL PROTECTED] wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... Calculation of eigenvalues and eigenvalues requires no assumption. However evaluation of the results IMHO implicitly assumes at least a unimodal distribution and reasonably homogeneous variance for the same reasons as ANOVA or regression. So think of th consequencesof calculating means and variances of a strongly bimodal distribution where no sample ocurrs near the mean and all samples are tens of standard devatiations from the mean. The largest number of standard deviations all data can be from the mean is 1. To get some data further away than that, some of it has to be less than 1 s.d. from the mean. Glen = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
M/G/1 model
I am studying the M/G/1 model for retrial queues. I know that 1 in M/G/1 means that there is a single server. Does anyone can tell me what M and G exactly stand for? Thanks in advance, Silvia = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: cigs figs
In article [EMAIL PROTECTED], Rich Ulrich [EMAIL PROTECTED] wrote: - re: some outstandingly confused thinking. Or writing. On Sat, 23 Jun 2001 15:25:31 GMT, mackeral@remove~this~first~yahoo.com (J. Williams) wrote: [ snip; Slate reference, etcetera ] ... My mother was 91 years old when she died a year ago and chain smoked since her college days. She defended the tobacco companies for years saying, it didn't hurt me. She outlived most of her doctors. Upon quoting statistics and research on the subject, her view was that I, like other do gooders and non-smokers, wanted to deny smokers their rights. What statistics would her view quote? to show that someone wants to deny smokers 'their rights'? [ Hey, I didn't write the sentence ] NO amount of demographic statistics can PROVE, even statistically, that smoking is harmful to the person doing it. Statistical arguments based on such data are at most indications, and may even be wrong. The woman who died recently at 120, a claimant for the title of the oldest living person, gave up smoking at the age of 114. I just love it, how a 'natural right' works out to be *exactly* what the speaker wants to do. That is essentially it. The only meaningful rights are the rights to do what others do not want you to do. And not a whit more. (Thomas and Scalia are probably going to give us tons of that bad philosophy, over the next decades.) What rights are denied to smokers? You know, you can't build your outhouse right on the riverbank, either. This only applies to second hand smoke, where the rights of others are directly involved. In some places, you can build your outhouse right on the riverbank; the only reason that you cannot or should not do so generally are that it would threaten others. Obviously, there is a health connection. How strong that connection is, is what makes this a unique statistical conundrum. How strong is that connection? Well, quite strong. Personally, I believe that there is a connection. But it is a situation where the prior probabilities of the various states make a big difference. I once considered that it might not be so bad to die 9 years early, owing to smoking, if that cut off years of bad health and suffering. Then I realized, the smoking grants you most of the bad health of old age, EARLY. (You do miss the Alzheimer's.) One day, I might give up smoking my pipe. Why are you smoking a pipe? Pipe smokers produce second hand smoke, and lots of objectionable odors. Can you cite any benefits which cigarette smokers cannot also claim? Everything involves risks and benefits, and the individual should decide. What is the statistical conundrum? I can almost imagine an ethical conundrum. (How strongly can we legislate, to encourage cyclists to wear helmets?) I sure don't spot a statistical conundrum. I see no statistical conundrum, either, but merely a situation where the regulators are using a very large amount of prior assumptions to justify the legislation. Now this does not mean that most of those assumptions may not be correct, but that this is what they are going by. I believe that one MUST use prior assumptions, as otherwise one will be strongly inconsistent, and it is even possible that nothing will be done. -- This address is for information only. I do not claim that these views are those of the Statistics Department or of Purdue University. Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399 [EMAIL PROTECTED] Phone: (765)494-6054 FAX: (765)494-0558 = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Help with stats please
In article 006901c0fce2$d07c7640$[EMAIL PROTECTED], Melady Preece [EMAIL PROTECTED] wrote: Hi. I am teaching educational statistics for the first time, and although I can go on at length about complex statistical techniques, I find myself at a loss with this multiple choice question in my test bank. I understand why the range of (b) is smaller than (a) and (c), but I can't figure out how to prove that it is smaller than (d). If you can explain it to me, I will be humiliated, but grateful. 1. Which one of the following classes had the smallest range in IQ scores? A) Class A has a mean IQ of 106 and a standard deviation of ll. B) Class B has an IQ range from 93 to 119. C) Class C has a mean IQ of 110 with a variance of 200. D) Class D has a median IQ of 100 with Q1 = 90 and Q3 = 110. The test bank says the answer is b. Melady What are the sizes of the classes? What are the distributions of the scores in the various classes? If the scores are random from some probability distribution, and other than the sample data there is no additional information about the actual scores, for other than extremely small classes (10 is large here), not many absolute statements can be made. I CAN tell that class C cannot have a smaller range than 29, because otherwise the variance cannot be 200, and scores are given as integers. If they are not integers, it goes down slightly. Even if the model is the totally untenable normal distribution, the scores are RANDOM, and the samples need not look at all normal. As to what was bothering you, what are the quantiles of the normal distribution? -- This address is for information only. I do not claim that these views are those of the Statistics Department or of Purdue University. Herman Rubin, Dept. of Statistics, Purdue Univ., West Lafayette IN47907-1399 [EMAIL PROTECTED] Phone: (765)494-6054 FAX: (765)494-0558 = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Marijuana
On Mon, 25 Jun 2001 09:09:52 GMT, [EMAIL PROTECTED] (Graaagh the Mighty) wrote: On Sun, 24 Jun 2001 14:39:06 GMT, [EMAIL PROTECTED] (David C. Ullrich) sat on a tribble, which squeaked: [1]That's one scary thing - in fact there are places in Windows95 where the system _regularly_ creates GPF's; something to do with thunking or something. [2]But the scary thing about the quote is that the guy was advocating _hiding_ AV's in programs we write instead of fixing them. AV's can be hard to debug - the eaiest way is to make certain they don't arise in the first place. And given this guy's attitude, one of the steps involved in ensuring that your code contains no hard-to-debug AV's is making sure you never use anything he wrote. Hence the sig - it's a public-service thing. Sometimes you can have access violations all the time and the program still works. (Michael Caracena, comp.lang.pascal.delphi.misc 5/1/01) And yet he never made the connection that maybe Michael Caracena's code *is* the code in Windows that regularly GPFs... Um, no. In [1] I wasn't talking about the GPF's that we see when Windows crashes. I forget the details, but these are _intentional_ GPF's that don't give error messages - they're part of how the system works. As opposed to [2] the GPF's this guy is hiding - these are not GPF's that are supposed to happen. (Seriously though -- core parts of Windoze are written in Pascal, and it is known that Windoze does hide some AVs it commits, especially those involving reading through a null pointer!) How do you know some parts are in Pascal, and what does that have to do with AV's? -- Bill Gates: No computer will ever need more than 640K of RAM. -- 1980 There's nobody getting rich writing software that I know of. -- 1980 This antitrust thing will blow over. -- 1998 Combine neo, an underscore, and one thousand sixty-one to make my hotmail addy. David C. Ullrich * Sometimes you can have access violations all the time and the program still works. (Michael Caracena, comp.lang.pascal.delphi.misc 5/1/01) = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: Help with stats please
Melady Preece wrote: Hi. I am teaching educational statistics for the first time, and although I can go on at length about complex statistical techniques, I find myself at a loss with this multiple choice question in my test bank. I understand why the range of (b) is smaller than (a) and (c), but I can't figure out how to prove that it is smaller than (d). If you can explain it to me, I will be humiliated, but grateful. I'm not sure why you would be humiliated, even if the answer were obvious. You can't prove the range of (b) is smaller than (d). The question isn't even worded clearly. (b) says a range of from 93 to 119 They range from 93 to 119 and have a range of 26 (subject to any typographical errors I might make!), but a range from to is just...sloppy. If (d) were a small class, say 2 students, the upper and lower quartiles could be 90 and 110, depending on the precise definition of quartile being used, and the range would be 20, even with normality, etc. 1. Which one of the following classes had the smallest range in IQ scores? A) Class A has a mean IQ of 106 and a standard deviation of ll. B) Class B has an IQ range from 93 to 119. C) Class C has a mean IQ of 110 with a variance of 200. D) Class D has a median IQ of 100 with Q1 = 90 and Q3 = 110. The test bank says the answer is b. = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Marijuana and heart attacks and similar research on sex
Recently, there was an extensive discussion about how to analyze data involving marijuana use and heart attacks. I just came across an interesting study that shows how to do a rigorous analysis in a very similar situation, the risk of heart attacks after sex. The actual paper appears in JAMA, but there is an excellent summary of it on the Bandolier web site: http://www.jr2.ox.ac.uk/bandolier/band30/b30-2.html This is a fun teaching example. Steve Simon, [EMAIL PROTECTED], Standard Disclaimer. STATS: STeve's Attempt to Teach Statistics. http://www.cmh.edu/stats Watch for a change in servers. On or around June 2001, this page will move to http://www.childrens-mercy.org/stats = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
Re: M/G/1 model
It's the Kendall notation A/B/C/D/E A interarrival time distribution M: exponential D: deterministic E: Erlang K G: General B Servive time distribution M: exponential D: deterministic E: Erlang K G: General C number of parallel servers D system capacity E queuing rules FIFO LIFO SIRO (servive in random order) PRI (priority) GD 'general discipline) M/G/1 stand for Exponential interaaival time/general servic time distribution/ 1 server Hope this help JCB France - Original Message - From: *Silvia* [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Monday, June 25, 2001 12:11 PM Subject: M/G/1 model I am studying the M/G/1 model for retrial queues. I know that 1 in M/G/1 means that there is a single server. Does anyone can tell me what M and G exactly stand for? Thanks in advance, Silvia = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ = = Instructions for joining and leaving this list and remarks about the problem of INAPPROPRIATE MESSAGES are available at http://jse.stat.ncsu.edu/ =
