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Re: adjusting marks

[Bob Hayden]

- Forwarded message from David A. Heiser -

I don't agree with Demming. Life is essentially a matter of diversity, and
being able to find one's own "niche". The process of ranking is inherent in
life whenever there is stress on a population. Going to college is indeed
"stress".

- End of forwarded message from David A. Heiser -

H.  In my department we are responding to a reviewer who urged
greater uniformity among sections of the same course.  I sort of
agree, but this has raised questions as to what should be the same and
what is allowed to vary.  Right now we have some sections of Stats.I
where weekly Minitab assignments are collected and graded and others
where computers are not used at all.  I don't think that is good.  On
the other hand, I don't think we all need to use the same text, as
long as we all use respectable ones -- say, ones on the approved list
for AP Stats.  While this is debatable, my outlook re education is
highly colored by my undergraduate experience at MIT.  There it was
common for the professor to give his (no women in those days) own idea
of what was important in his field.  These views were often highly
idiosyncratic and absolutely brilliant.  I had courses containing
stuff that was not contained in any published textbook.  I loved it
and learned a lot.  Enforcing uniformity would have turned MIT into
just another college.

Now, what do you think about the variation in Beethoven's symphonies?
Obviously this guy did not have a very good QC system.  There is a lot
more uniformity in performance these days -- I hear little differences
compared to the differences among Toscanini, Walter, Furtwangler,
Mengelberg, etc.  Is this really an improvment?

Likewise cars are all much more alike than they were when we have
inline 6s and 8s, v-8s, v-12s, OHV engines, flatheads, etc.  Maybe
it's for the better but I miss my Buick straight eight.
 
What about spouses?  Should they all be the same?

  _
 | |  Robert W. Hayden
 | |  Department of Mathematics
/  |  Plymouth State College MSC#29
   |   |  Plymouth, New Hampshire 03264  USA
   | * |  Rural Route 1, Box 10
  /|  Ashland, NH 03217-9702
 | )  (603) 968-9914 (home)
 L_/  [EMAIL PROTECTED]
  fax (603) 535-2943 (work)

Re: adjusting marks

[Jim Clark]

Hi

On Tue, 21 Dec 1999, Peter Westfall wrote:
> Regarding making the standard deviation large, Deming would say that
> management's (professors, administrators) job entails minimizing
> variation among students.  This can be done in the usual ways -
> admissions procedures, advising, prerequisites.  Individual classes are
> "processes" within the larger system, and in the process of continual
> improvement, one seeks ways to minimize variation within the processes.
> Deming shows a diagram where the knowledge of people before training is
> scattered and highly variable, and after training the mean level is
> higher but the variation smaller.  The inference is that the more
> effective the classroom experience, the less variation in the final
> levels of knowledge and abilities of the students, as they pertain to the
> subject at hand.

Artificially giving all students (or almost all) the same grade
does not minimize variation in the underlying trait, achievement,
in this case. It simply hides the variation so that one does not
know to what extent one is minimizing differences in achievement,
and rewards students for not trying to achieve more than some
minimal level.

> My question is again: Is ranking really necessary?  Given the goal of
> reducing variation, what does it help? Students in competition for the
> scarce A's will withhold information from one another.  Does this achieve
> the stated aim of the system in an optimal way?  W. Edwards Deming would
> have said, most emphatically, no.  He spoke quite often of the
> educational system particularly in his later years; his message was not
> at all meant to be limited to manufacturing.

Grading is not equivalent to ranking, unless one uses a forced
distribution.  One can grade without any restriction on the
number of As or other grades other than the achievement of the
students.  I would be interested in hearing about any empirical
evidence that non-use of grading schemes produces better or even
as good learning as the use of grades?

Best wishes
Jim


James M. Clark  (204) 786-9757
Department of Psychology(204) 774-4134 Fax
University of Winnipeg  4L05D
Winnipeg, Manitoba  R3B 2E9 [EMAIL PROTECTED]
CANADA  http://www.uwinnipeg.ca/~clark

Re: Difference between means

[DIAMOND Mark]

Rich Ulrich wrote in message ...
>On Tue, 21 Dec 1999 09:34:53 +0800, "DIAMOND Mark" <[EMAIL PROTECTED]>
>wrote:
>Well, Mr Noname@noname, since I can't write to an address.
>And I will follow an example that I read lately and say that I don't
>feel kindly towards people who don't give a name and e-mailing
>address.

Point taken. My apologies for the lack of email address, although my name is
correct. Normally my signature file with a spam avoiding email address is
included. I do not know why it was not in this instance. Maybe an
interaction between Microsoft product reliablility and the inscrutable
workings of providence. University policy is to avoid putting email
addresses that can be extracted by spammers in the body of newsgroup
postings.

Mark R Diamond
Vision Research Laboratory
The University of Western Australia
no spam email: markd at psy dot uwa dot edu dot au


>I will have
>to say publicly that you did a lousy job of asking the question.  Or,
>maybe it particularly looks that way because it is  data from a lousy
>design.

Quite possibly. I shall try again.


(1) A prior experiment  shows that a particular (special) subject who
engages in a temporal bisection experiment in which she is asked to say
whether a probe bar appeared early or late in temporal interval can do so
extremely accurately. That is, if the interval is, say 500 ms long, and a
probe stimulus is flashed 297 ms after the appearance of the stimulus that
marks the beginning of the interval, then she will (with almost no errors)
say that the stimulus was probe stimulus was early. Similarly, if the probe
appears 503 ms after the first stimulus, she will say that the probe was
late.
(2) Theory, and some other results, predicts that, for this subject, if her
attention is disturbed by an event that occurs in the first half of the
interval, then she will judge the midpoint of the interval to be later than
it really is. In other words, she will say that probes appearing up to 265
ms after the beginning of the interval will be judged to be early, and
probes appearing after 271 ms will be judged to be late. A reversal of
prediction occurs for conditions in which the disturbance happens in the
latter half of the interval.

How does one go about testing this prediction?

Re: adjusting marks

[Bob Hayden]

- Forwarded message from Peter Westfall -

Bob Hayden wrote:

> - Forwarded message from Peter Westfall -
>
> Deming himself (if I remember correctly) graded everyone as "A" until
> the administration noticed, and then they made his courses Pass-Fail.
>
> Deming was also very much against ranking students in any way, except
> for the possible exception of identifying an exceptional student that
> others might emulate (the > 3*sigma student) and identifying the
> exceptionally poor student (< 3*sigma) for remediation.  All other
> students should be be essentially equivalent, in Deming's philosophy.
>
> - End of forwarded message from Peter Westfall -
>
> Would you recommend this for drivers' license tests?  Oh, I get it,
> that's what we're doing already!  No wonder.
>
> I have to admit, it would sure simplify quality control if we
> considered anything within +- 3 s.d. to be OK.  Then I guess the
> motivation would be to throw in a few clunkers now and then to keep

> the s.d. as large as possible?

Bob,

Your remarks sound facetious. I was hoping to stimulate some serious
discussion.  Have you read anything by Deming?

Here is Deming's philosophy, as well as I can paraphrase it for the
present situation:

Students/teachers/administrators form a system. The system has an aim,
which is (presumably) to educate everyone as well as possible, for the
good of the students, and for the good of society.  What good does
ranking do?  Does it help to achieve the aim of the system?  Or rather,
is it simply a weeding process?  Is ranking necessary? (these are mainly
Deming's words, but I must admit I see lots of value there.)

Regarding making the standard deviation large, Deming would say that
management's (professors, administrators) job entails minimizing
variation among students.  This can be done in the usual ways -
admissions procedures, advising, prerequisites.  Individual classes are
"processes" within the larger system, and in the process of continual
improvement, one seeks ways to minimize variation within the processes.
Deming shows a diagram where the knowledge of people before training is
scattered and highly variable, and after training the mean level is
higher but the variation smaller.  The inference is that the more
effective the classroom experience, the less variation in the final
levels of knowledge and abilities of the students, as they pertain to the
subject at hand.

My question is again: Is ranking really necessary?  Given the goal of
reducing variation, what does it help? Students in competition for the
scarce A's will withhold information from one another.  Does this achieve
the stated aim of the system in an optimal way?  W. Edwards Deming would
have said, most emphatically, no.  He spoke quite often of the
educational system particularly in his later years; his message was not
at all meant to be limited to manufacturing.


Peter



Where I teach, surveys of students show their number one reason for
being here is "for the social life".  I can assure you that if I
automatically gave everyone As the students would act to maximize
their goal of a good social life and no one would even attend class.

Education also serves some sort of certification purpose.  Presumably
a diploma means something more than "this person paid tuition" since a
receipt would do for that.  I would have no problem with no grading as
long as there is also no diploma.

Grades (or at least some measure of student learning) also provides
feedback to the instructor.  This is where Deming seems inconsistent
here.  Giving everyone an A seems like declaring that every part
passes inspection -- by fiat.  What kind of quality control system is
that? 

  _
 | |  Robert W. Hayden
 | |  Department of Mathematics
/  |  Plymouth State College MSC#29
   |   |  Plymouth, New Hampshire 03264  USA
   | * |  Rural Route 1, Box 10
  /|  Ashland, NH 03217-9702
 | )  (603) 968-9914 (home)
 L_/  [EMAIL PROTECTED]
  fax (603) 535-2943 (work)

Re: adjusting marks

[David A. Heiser]

- Original Message -
From: Peter Westfall <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, December 21, 1999 6:45 PM
Subject: Re: adjusting marks


>
>
> Bob Hayden wrote:
>
> > - Forwarded message from Peter Westfall -
> >
> > Deming himself (if I remember correctly) graded everyone as "A" until
> > the administration noticed, and then they made his courses Pass-Fail.
> >
> > Deming was also very much against ranking students in any way, except
> > for the possible exception of identifying an exceptional student that
> > others might emulate (the > 3*sigma student) and identifying the
> > exceptionally poor student (< 3*sigma) for remediation.  All other
> > students should be be essentially equivalent, in Deming's philosophy.
> >
> > - End of forwarded message from Peter Westfall -
> >
> > Would you recommend this for drivers' license tests?  Oh, I get it,
> > that's what we're doing already!  No wonder.
> >
> > I have to admit, it would sure simplify quality control if we
> > considered anything within +- 3 s.d. to be OK.  Then I guess the
> > motivation would be to throw in a few clunkers now and then to keep
>
> > the s.d. as large as possible?
>
> Bob,
>
> Your remarks sound facetious. I was hoping to stimulate some serious
> discussion.  Have you read anything by Deming?
>
> Here is Deming's philosophy, as well as I can paraphrase it for the
> present situation:
>
> Students/teachers/administrators form a system. The system has an aim,
> which is (presumably) to educate everyone as well as possible, for the
> good of the students, and for the good of society.  What good does
> ranking do?  Does it help to achieve the aim of the system?  Or rather,
> is it simply a weeding process?  Is ranking necessary? (these are mainly
> Deming's words, but I must admit I see lots of value there.)
>
> Regarding making the standard deviation large, Deming would say that
> management's (professors, administrators) job entails minimizing
> variation among students.  This can be done in the usual ways -
> admissions procedures, advising, prerequisites.  Individual classes are
> "processes" within the larger system, and in the process of continual
> improvement, one seeks ways to minimize variation within the processes.
> Deming shows a diagram where the knowledge of people before training is
> scattered and highly variable, and after training the mean level is
> higher but the variation smaller.  The inference is that the more
> effective the classroom experience, the less variation in the final
> levels of knowledge and abilities of the students, as they pertain to the
> subject at hand.
>
> My question is again: Is ranking really necessary?  Given the goal of
> reducing variation, what does it help? Students in competition for the
> scarce A's will withhold information from one another.  Does this achieve
> the stated aim of the system in an optimal way?  W. Edwards Deming would
> have said, most emphatically, no.  He spoke quite often of the
> educational system particularly in his later years; his message was not
> at all meant to be limited to manufacturing.
>
>
> Peter
>
---
Very Intersting


I don't agree with Demming. Life is essentially a matter of diversity, and
being able to find one's own "niche". The process of ranking is inherent in
life whenever there is stress on a population. Going to college is indeed
"stress".

If in order to suceed, I need to obtain a PhD from Stanford, then I have to
get high grades and attain other acheivments to get in that few percent that
gets accepted. If my college grades are all "pass", how am I going to
compete with the applicate with A+++ grades from NCU?

How are new hires for the expensive New York/Washington law firms hired? Not
on pass/fail but on which law school and how the professors rated the
student  and what were the extra curricular activities? Much of this is
subjective, but when you have 300 applicants for one job, you have to do
some ranking to pick the top 3 or 5.

Demming I think has the quality control mindset of pass/fail in terms of
manufactured objects, where everything is acceptable between -3 and +3 sigma
(Now it is -6 to +6 sigma.) This may be fine for shop work on the floor. In
this country the only thing we manufacture now is credit and money to buy
manufactured goods from other countries.

You need a very diverse population now. The process of ranking as flawed as
it is, works, because there are so many areas where one can find his own
niche, and ranking is one way of finding one's niche.

DAH

Re: adjusting marks

[Peter Westfall]

Bob Hayden wrote:

> - Forwarded message from Peter Westfall -
>
> Deming himself (if I remember correctly) graded everyone as "A" until
> the administration noticed, and then they made his courses Pass-Fail.
>
> Deming was also very much against ranking students in any way, except
> for the possible exception of identifying an exceptional student that
> others might emulate (the > 3*sigma student) and identifying the
> exceptionally poor student (< 3*sigma) for remediation.  All other
> students should be be essentially equivalent, in Deming's philosophy.
>
> - End of forwarded message from Peter Westfall -
>
> Would you recommend this for drivers' license tests?  Oh, I get it,
> that's what we're doing already!  No wonder.
>
> I have to admit, it would sure simplify quality control if we
> considered anything within +- 3 s.d. to be OK.  Then I guess the
> motivation would be to throw in a few clunkers now and then to keep

> the s.d. as large as possible?

Bob,

Your remarks sound facetious. I was hoping to stimulate some serious
discussion.  Have you read anything by Deming?

Here is Deming's philosophy, as well as I can paraphrase it for the
present situation:

Students/teachers/administrators form a system. The system has an aim,
which is (presumably) to educate everyone as well as possible, for the
good of the students, and for the good of society.  What good does
ranking do?  Does it help to achieve the aim of the system?  Or rather,
is it simply a weeding process?  Is ranking necessary? (these are mainly
Deming's words, but I must admit I see lots of value there.)

Regarding making the standard deviation large, Deming would say that
management's (professors, administrators) job entails minimizing
variation among students.  This can be done in the usual ways -
admissions procedures, advising, prerequisites.  Individual classes are
"processes" within the larger system, and in the process of continual
improvement, one seeks ways to minimize variation within the processes.
Deming shows a diagram where the knowledge of people before training is
scattered and highly variable, and after training the mean level is
higher but the variation smaller.  The inference is that the more
effective the classroom experience, the less variation in the final
levels of knowledge and abilities of the students, as they pertain to the
subject at hand.

My question is again: Is ranking really necessary?  Given the goal of
reducing variation, what does it help? Students in competition for the
scarce A's will withhold information from one another.  Does this achieve
the stated aim of the system in an optimal way?  W. Edwards Deming would
have said, most emphatically, no.  He spoke quite often of the
educational system particularly in his later years; his message was not
at all meant to be limited to manufacturing.


Peter


>
>
>
>   _
>  | |  Robert W. Hayden
>  | |  Department of Mathematics
> /  |  Plymouth State College MSC#29
>|   |  Plymouth, New Hampshire 03264  USA
>| * |  Rural Route 1, Box 10
>   /|  Ashland, NH 03217-9702
>  | )  (603) 968-9914 (home)
>  L_/  [EMAIL PROTECTED]
>   fax (603) 535-2943 (work)

Re: adjusting marks

[Bob Hayden]

- Forwarded message from Peter Westfall -

Deming himself (if I remember correctly) graded everyone as "A" until
the administration noticed, and then they made his courses Pass-Fail.

Deming was also very much against ranking students in any way, except
for the possible exception of identifying an exceptional student that
others might emulate (the > 3*sigma student) and identifying the
exceptionally poor student (< 3*sigma) for remediation.  All other
students should be be essentially equivalent, in Deming's philosophy.

- End of forwarded message from Peter Westfall -

Would you recommend this for drivers' license tests?  Oh, I get it,
that's what we're doing already!  No wonder.

I have to admit, it would sure simplify quality control if we
considered anything within +- 3 s.d. to be OK.  Then I guess the
motivation would be to throw in a few clunkers now and then to keep
the s.d. as large as possible? 
 

  _
 | |  Robert W. Hayden
 | |  Department of Mathematics
/  |  Plymouth State College MSC#29
   |   |  Plymouth, New Hampshire 03264  USA
   | * |  Rural Route 1, Box 10
  /|  Ashland, NH 03217-9702
 | )  (603) 968-9914 (home)
 L_/  [EMAIL PROTECTED]
  fax (603) 535-2943 (work)

Re: adjusting marks

[Peter Westfall]

dennis roberts wrote:

> 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

I agree with Dennis, and would like to chime in with some other points.

The late W. Edwards Deming stated that the use of a forced distribution for
grades is "ruinous" to the entire system of education.  It seems to me that
grading "on the curve" is in some sense an attempt at using a forced
distribution.  (And if the goal is indeed to enforce a distribution, then use the
ranked data, not the normal distribution; see below for more about ranking.)

Use of a forced distribution creates a win-lose scenario for the students.  If we
are to improve as educators, we need to seek win-win scenarios.  Deming himself
(if I remember correctly) graded everyone as "A" until the administration
noticed, and then they made his courses Pass-Fail.

Deming was also very much against ranking students in any way, except for the
possible exception of identifying an exceptional student that others might
emulate (the > 3*sigma student) and identifying the exceptionally poor student (<
3*sigma) for remediation.  All other students should be be essentially
equivalent, in Deming's philosophy.

I would be curious to hear what others have to say about this. Is Deming still
with us?  And how can we create win-win teaching strategies that will also
satisfy administrators?


Peter

Re: adjusting marks

[EAKIN MARK E]

Dennis writes:
> 
> 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!
> 
> 

To this I agree and it is my position also. Grading is subjective. You can
leave the grades alone and subjectively decide on the cut-off points,
leave the cut-off points fixed and subjectively decide on adding points to
all grades, in non-objective tests you can decide how much to count
off, etc. 

Which doesn't even consider the fact that few (no one I know of)
instructors attempt to validate their testing instruments using the
concepts of measurement theory (reliablity and validity assesment). This
is another thread I would like to see discussed. Shouldn't we teach our
Ph.D. students how to use measurement theory in the area that of
measuring that they will practice most often: measuring student
performance? 




 Mark Eakin 
Associate Professor
Information Systems and Management Sciences Department
University of Texas at Arlington
[EMAIL PROTECTED] or
[EMAIL PROTECTED]

Re: adjusting marks

[dennis roberts]

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

Re: adjusting marks

[EAKIN MARK E]

Dennis Roberts writes:
> 
> 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 ...
> 

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

 grade = function(acquired information, other variables) + error  

where acquired information (information gained in this class or others)
can be expressed at any level of Bloom's taxonomy of educational 
objectives (i.e., from  simple recall of information all the way
to evaluation),

  other variables include differences in tests from one
 semester to the next, differences in presentation, etc.

  and the error term might just as well be incorporated into the set
 of "other variables". 

I believe that the marginal function of grades and information is
positively monotonic but not necessarily first-order (does a student who
made an 80 contain twice as much information as a student who make a 40?)

Therefore I often check my grade distribution to see if it matches 
my expectations. I feel that classes containing more than 60
students should contain a typical mix of good and bad students. So if my
grade distribution suddenly drops in one semester, I will try to determine
the reason and add points if I feel that the difference is a result of
variables other than changes in students' information. For small classes 
this is much more complicated. Luckily, it is easier to get to know
more about each student in a small class and from that knowledge I have a
better feel for what is causing the grade distribution to be higher or
lower than my expectations. 

While I do not grade on a curve, I feel that if reasons exist,it is more
valid to adjust atypical grades distributions than not to adjust them. 
My reason for not grading on a curve is more for class harmony. Grading on
a curve often means taking points away from some students while adding to
others. I noticed that a class can suddenly become hostile if some
students are treated better than others. This hostile environment can be
detrimental to a class's performance also.

Re: chi sq & arbitrary sample size

[Rich Ulrich]

On 19 Dec 1999 21:19:19 -0800, [EMAIL PROTECTED] (Donald F.
Burrill) wrote:

> On 18 Dec 1999, Archtopist wrote:
> 
> > Happy holidays!  I am developing a map of the annual probability of
> > burning (in a wildfire) for a mountainous area.  I have a map with 
> > cells labeled according to 
> > a) one of five vegetation types and 
> > b) housing density and 
> > c) the year(s) when wildfire occurred in the cell. 
> > I want to find out if there are differences in the likelihood of fire 
> > depending on vegetation and housing density. 
> 
> Sounds daunting.  If your timeline is long enough, neither vegetation 
> type nor housing density will be constant, and it is possible that 
> housing density may be changing even for relatively short timelines, 
> almost certainly changing at different rates in different cells.  (After 
> all, if you go far enough back, housing density = 0 for all cells...)
 [ ...]

I like everything Donald says here, and also in the part I snipped.
The longer I look at the question, though, the more it seems to me
that any simple approach is terribly naive or probably horribly
political at the same time.  What is the underlying question -- WHO
should be allowed to intrude into WHAT wilderness areas?

If the question is already undergoing a hot debate, you have to carry
out a study which responds to the concerns of the debate.  Unless
someone has a motive for presenting some specious numbers, which is
what you must get from a non-responsive survey.

Then there is the biology which humans are interfering with.  Certain
pines need the area to be burnt-out in order for their seeds to
propagate, so it ought to be at least once per century (I think it
was).  If there is a natural burn-over rate, how much are humans
interfering with it, or how much *should* humans interfere?

I sure would hope that firefighters have at least a little bit of
effectiveness, so that for areas that are identical except that some
acres have homes (and will be protected), the ones with homes have
fewer fires.

-- 
Rich Ulrich, [EMAIL PROTECTED]
http://www.pitt.edu/~wpilib/index.html

Re: Prediction Model Question

[Frank E Harrell Jr]

"Donald F. Burrill" wrote:

> Inicidentally, I'd strongly recommend constructing interaction variables
> that are orthogonal at least to their own main effects (and lower-order
> interactions, when there are any), and possibly orthogonal to some or all
> of the apparently irrelevant other predictors.  Else correlations between
> the interaction variables and other variables can, sometimes, be horribly
> confusing;  especially with the "quantitative" (non-categorical)
> variables, whose products with other such variables are likely to be
> strongly (positively) correlated with the original variables merely
> because the original variables tend to be always positive and sometimes
> far from zero -- thus inducing what I've elsewhere called "spurious
> multicollinearity".

This I do not understand.  I don't see the point in testing main effects
in the presence of interaction effects (unlike the pooled main effect +
interaction
effect tests which are completely invariant to coding).  So I don't see
why coding matters.  -Frank Harrell

Re: adjusting marks

[J. Williams]

I assume she intends to move all marks up or down in tandem.  I assume too 
that the marks themselves are quantitative along some sort of continuum.  
Regardless, the easiest thing would be to rank order them and make a decision 
where the cutoff lines for A's, B's, etc.make sense.   I don't see this as a 
statistical problem per se.  You could graph the scores with a scatterplot or 
histogram to determine the shape of the distribution.  She could visually 
inspect the plot and see if the distribution is bell-shaped, uniform, skewed, 
etc.  If the data so indicate, one could do Z scores and find out the distance 
from the mean, percentile rank, etc., but IMHO this problem can be better 
solved by intuition, viz., looking at the data, drawing rational cutoff lines 
and at the same time being fair to the students.


In article , "Generic" 
<[EMAIL PROTECTED]> 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!
>
>

Re: USAF training (was: teaching stat. ... by rules?

[Donald F. Burrill]

On 21 Dec 1999, R.W. Hutchinson wrote:

> There are persistent rumours that the U.S. Air Force, which has a
> massive educational system, including teacher-training, does a far and
> away better job of "education" than the "public school system."  You 
> don't have to be outstandingly intelligent to join the Air Force, 
> either, and it seems to be able to cope with a wide variety of students. 
 
>   a) are the rumours false?

I don't know empirically, but 'twouldn't surprise me if they were true.

>   b) if not, is the success a function of subject matter rather 
>  than their approach to teaching, and hence presumably 
>  inapplicable to teaching Statistics?

My guess would be, neither of the above.  People in the Air Force want to 
be there.  If they don't successfully learn what the AF wants them to 
learn, they won't be there.  Classic example of motivation, that would 
probably overcome even pretty bad teaching.  But the instructors also 
want to be where they are, and if they show up as incompetent, they won't 
be there.  So there's motivation on both sides of the classroom fence.

>   I am not, nor have I ever been, in the Air Force, and hence I am 
> unable to shed any light on the matter, but for DECADES I have been 
> picking up rumours that something about their educational system WORKS. 

Where there's a lot of persistent smoke, there very well may be a fire.

 
 Donald F. Burrill [EMAIL PROTECTED]
 348 Hyde Hall, Plymouth State College,  [EMAIL PROTECTED]
 MSC #29, Plymouth, NH 03264 603-535-2597
 184 Nashua Road, Bedford, NH 03110  603-471-7128  

Re: Difference between means

[Rich Ulrich]

On Tue, 21 Dec 1999 09:34:53 +0800, "DIAMOND Mark" <[EMAIL PROTECTED]>
wrote:

> I have a problem which, in the end, comes down to making an inference about
> a difference between means, but it seems more complicated than any example I
> can find in Croxton's Applied General Statistics or Sach's Applied
> Statistics: Handbook of techniques.
> 
> Subjects make dichotomous judgements, coded 0 or 1, in two quite different
> conditions. The judgement concerns whether the appearance of a probe bar in
> a 1 second interval was closer to the beginning of the interval or to the

Well, Mr Noname@noname, since I can't write to an address, I will have
to say publicly that you did a lousy job of asking the question.  Or,
maybe it particularly looks that way because it is  data from a lousy
design.  

And I will follow an example that I read lately and say that I don't
feel kindly towards people who don't give a name and e-mailing
address.

Is all your analysis on one person?
Is there any consideration of RIGHT vs WRONG judgment about which is
closer (which is an obvious aspect, which goes unmentioned)?  or is
this solely a comparison of means (which is okay, but different)?

That might be so straightforward that it is trivial.  However,  there
is a huge potential for gaining strength in the comparisons, by
pairing the answers according to position of the probe bar in the
interval -- or otherwise modeling by the position.

Then there is the prospect that you have multiple persons doing the
trials.

-- 
Rich Ulrich, [EMAIL PROTECTED]

http://www.pitt.edu/~wpilib/index.html

Re: adjusting marks

[Bob Davies]

[EMAIL PROTECTED] writes:
>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!
>
Use a calculator to find the average and the standard deviation of the
grades that she has.  Then have her decide what grade she wants to be the
average of her adjusted class grades.  She also needs to decide what
standard deviation she wants for her new grades.  (I often use 80 as the
new average and 7 as the standard deviation.) Now, here is how to figure
the new grades:

new grade =[(old grade - old average)/old standard deviation]* new
standard deviation + new average.

For my scale, indicated above, the formula becomes

y = (x - avg)* 7 + 80

Hope this helps.

RGD
>
>--
>
>
>
>



Robert G. Davies
Woodberry Forest School
Woodberry Forest, VA  22989
(540) 672-3900

Re: Standards for "Skewness"

[Robert Dawson]

Ronald B. Livingston asked:

>Are there "standards" for describing the skew of a distribution?  For
>example, 0 to 1 = mild; 1 - 2 = moderate, etc.  I am aware of tests of
>significance for skew, but with large samples practically any skew is
>significant. Any references would be appreciated.

One possibility would be to see what transformation (if any) would
symmetrize the distribution (or remove its skewness, anyhow).  This is not
quite what you asked for, but might have advantages.

-Robert Dawson

Re: Christmas Reading?

[Graham D Smith]

Last vacation I enjoyed reading Jostein Gaarder's "Sophie's World" which is
an engaging and thought-provoking introduction to philosophy presented in
the form of a novel. I can also recommend the following two books on
mathematics and two other books on philosophy.

John Allen Paulos "A Mathematician Reads the Newspaper"
Rudy Rucker "The Fourth Dimension and How to Get There"

Daniel Dennett "Consciousness Explained" (Philosophy of Mind)
Robin Dunbar "The Trouble with Science" (Philosophy of Science)

However, I shall be reading "The Meme Machine" by Susan Blackmore.

Merry Christmas and a Happy New Year

Graham

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]

RE: Christmas Reading?

[Tatikola, Kanaka [PRI]]

I personally like THE HISTORY OF STATISTICS , The measurement of
uncertainity before 1900, by Stephen M. Stigler.

Kanaka

-Original Message-
From:   pbern10 [SMTP:[EMAIL PROTECTED]]
Sent:   Thursday, December 16, 1999 1:35 PM
To: Humberto Barreto; Graham Clarke; [EMAIL PROTECTED]
Subject:Re: Christmas Reading?

Humberto Barreto wrote on 12/16/99 6:29 AM:

>>Does anyone know of a book on statistics (or maths) that likewise
is a
>>good non-technical read?  perhaps about some statistical
'characters' or
>>perhaps history of statistics.
>
>I bet you'd like James Gleick's stuff:
>
>Chaos: Making a New Science (1988)
>Genius (a bio of Richard Feynman) (1993)
>and his latest
>Faster: The Accelaration of Just About Everything, which I've just
started.
>
>Happy holidays!

The Cartooon Guide to Statistics by Larry Gonick is excellent. I 
recommend it to statistics students who are getting bogged down in
the 
prose of more detailed texts. It has both history and humor yet 
accurately conveys the fundamental concepts of statistics.

Paul Bernhardt

Re: adjusting marks

[dennis roberts]

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: teaching statistical methods by rules?

[R.W. Hutchinson]

Sorry to get so close to "off topic" but:

There are persistent rumours that the U.S. Air Force, which has a massive educational
system, including teacher-training, does a far and away better job of "education"
than the "public school system." You don't have to be outstandingly intelligent to
join the Air Force, either, and it seems to be able to cope with a wide variety of
students.

a) are the rumours false?

b) if not, is the success a function of subject matter rather than their
approach to teaching, and hence presumably inapplicable to teaching Statistics?

I am not, nor have I ever been, in the Air Force, and hence I am unable to
shed any light on the matter, but for DECADES I have been picking up rumours that
something about their educational system WORKS.
--
"I would predict that there are far greater mistakes waiting
to be made by someone with your obvious talent for it."
Orac to Vila. [City at the Edge of the World.]
---
R.W. Hutchinson. | [EMAIL PROTECTED]

Re: algorithm for cumulative t-distribution

[R.W. Hutchinson]

>I am trying to write some code which will churn
>out a set of values representing the cumulative
>density function of the Student t-distribution,
>for a given probability and range of DFs.
>
>Can anyone tell me what I should be trying to
>code?
>
>I can find dozens of tables which list the values
>I want, and dozens of applets which generate the
>values I want, but I need an algorithm which will
>allow me to generate these values on the fly,
>given the user's "certainty".
>
>I need to know which "X value" corresponds to
>given "area under the t-distribution".
>
>Any pointers to papers or URLs, would be much
>appreciated.

What you are looking for, turns out to be a finite sum of trigonometric 
functions.
They can be found e.g. in the Johnson & Kotz books on "Distributions."
--
"I would predict that there are far greater mistakes waiting
to be made by someone with your obvious talent for it."
Orac to Vila. [City at the Edge of the World.]
---
R.W. Hutchinson. | [EMAIL PROTECTED]

statistics with excel

[Andreas Stadie]

I'm intressted in working with excel addins.

does anyone have experiences with that or can give me helpful links?

Any input would be appreciated.

Please respond to [EMAIL PROTECTED] so we don't overload the group.

Andreas Stadie

Re: meeting probability question

[Erik Max Francis]

"Patrick D. Rockwell" wrote:

> Avi Lev wrote:
>
> > this translates into: P = SIG[i=1..n](PI[j=1,j!=i..n] (dj)) -
> 
> Hi. What is j! ? I know what the PI operator is, but what does
> PI[j=1,j!=1..n] do?

I would guess j = 1 to n, excluding j = i.

-- 
   Erik Max Francis | icq 16063900 | email [EMAIL PROTECTED]
Alcyone Systems | web http://www.alcyone.com/max/
   San Jose, CA | languages en, eo | icbm 37 20 07 N 121 53 38 W
USA | 377 days left | &tSftDotIotE
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/  \ Things are as they are because they were as they were.
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