Re: 10 envelopes, 10 persons

[Glen Barnett]

Stan Brown wrote:
> 
> Problem posed me by a student: ten persons (A through J) and ten
> envelopes containing cards marked with letters A through J. (Each
> letter is in one and only one envelope.)
> 
> The random variable x is the number of people who get the "right"
> envelope when the envelopes are handed out randomly. Obviously
> 0 <= x <= 10.
> 
> Question: How do we express the probability distribution P(x)?
> 
> I've done some work on this, and I _must_ be missing something
> obvious. Here's part what I've got so far.
> 
> 10! = number of possible arrangements. Only one of them assigns all
> ten envelopes to the right people, so
> P(10) = 1/10!
> 
> If nine people get the right envelopes, the tenth must also get the
> right envelope. So
> P(9) = 0
> 
> I bogged down on figuring P(8), though. Then I tried to look at P(0)
> and got even more bogged down.
> 
> Am I missing something here? Is there an elegant way to write
> expressions for the probabilities of the various x's?

This is sometimes called the matching problem or the matching
experiment.

Type "letters envelopes random" into google and you get several
relevant hits - e.g. 
http://www.math.uah.edu/stat/urn/urn6.html
http://www.wku.edu/~neal/probability/matching.html 

either of these might be enough for you to see how to do it.

If you put "matching" in there as well it would probably
target your search better, but I just wanted to show you
you didn't need more than your own description of the
problem to find out lots just with google.

Glen


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

10 envelopes, 10 persons

[Stan Brown]

Problem posed me by a student: ten persons (A through J) and ten 
envelopes containing cards marked with letters A through J. (Each 
letter is in one and only one envelope.)

The random variable x is the number of people who get the "right" 
envelope when the envelopes are handed out randomly. Obviously 
0 <= x <= 10.

Question: How do we express the probability distribution P(x)?

I've done some work on this, and I _must_ be missing something 
obvious. Here's part what I've got so far.

10! = number of possible arrangements. Only one of them assigns all 
ten envelopes to the right people, so 
P(10) = 1/10!

If nine people get the right envelopes, the tenth must also get the 
right envelope. So
P(9) = 0

I bogged down on figuring P(8), though. Then I tried to look at P(0) 
and got even more bogged down.

Am I missing something here? Is there an elegant way to write 
expressions for the probabilities of the various x's?

-- 
Stan Brown, Oak Road Systems, Cortland County, New York, USA
  http://oakroadsystems.com
My reply address is correct as is. The courtesy of providing a correct
reply address is more important to me than time spent deleting spam.


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: biostatistics careers

[A.J. Rossini]

> "RS" == Richard Seymann <[EMAIL PROTECTED]> writes:

RS> And if I may muddy the waters even more, what is the
RS> difference between biostatistics and biometry?  Dick

Depends on which definition of "biometry" you are using.  One
definition used to be an older name for what is now biostatistics (and
what might again become biometry, according to how some in the field
want to rename it again to make it more relevant to measurement and
design).  That's a nice murky response, which shows how our language
is ill-defined.

There are other definitions, which have little to do with statistics. 

best,
-tony

-- 
A.J. RossiniRsrch. Asst. Prof. of Biostatistics
U. of Washington Biostatistics  [EMAIL PROTECTED]
FHCRC/SCHARP/HIV Vaccine Trials Net [EMAIL PROTECTED]
-- http://software.biostat.washington.edu/ --
FHCRC: M-W: 206-667-7025 (fax=4812)|Voicemail is pretty sketchy/use Email
UW:   T-Th: 206-543-1044 (fax=3286)|Change last 4 digits of phone to FAX
Rosen: (Mullins' Lab) Fridays, and I'm unreachable except by email.


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

RE: Maximized lambda4

[Wuensch, Karl L]

Dennis asked "how do we know what a test's true reliability is?"

Osburn knew because he simulated true-score covariance matrices and
from these obtained observed score covariance matrices as a function of the
true-score matrices and hypothetical values of reliability.  More details
are in his article in Psychological Methods, 2000, 5, 343-355.

Karl W.



=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: Maximized lambda4

[Dennis Roberts]

At 01:49 PM 11/19/01 -0500, Wuensch, Karl L wrote:
> Callender and Osburn (Educational and Psychological Measurement,
>1977, 37, 819-825) developed a method for estimating maximized lambda4, the
>greatest split-half reliability coefficient among all possible split halves
>for a scale.  The method is quite tedious to do by hand, and the authors
>provided a FORTRAN program for accomplishing it.  Not having a FORTRAN
>compiler, I'm considering writing an SAS program (IML) to do this, but don't
>want to waste my time reinventing the wheel if someone else has already
>written an SAS or SPSS program for this purpose.  If you are aware of any
>such program, please advise me.  Thanks.
>
> By the way, Callender and Osburn's work indicates that maximized
>lambda4 is a much better estimate of a test's true reliability than is
>lambda3 (coefficient alpha).

how do we know what a test's true reliability is?



>  ~~~
>Karl L. Wuensch, Department of Psychology,
>East Carolina University, Greenville NC  27858-4353
>Voice:  252-328-4102 Fax:  252-328-6283
>mailto:[EMAIL PROTECTED] 
>http://core.ecu.edu/psyc/wuenschk/klw.htm
>
>
>
>
>=
>Instructions for joining and leaving this list and remarks about
>the problem of INAPPROPRIATE MESSAGES are available at
>   http://jse.stat.ncsu.edu/
>=

_
dennis roberts, educational psychology, penn state university
208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED]
http://roberts.ed.psu.edu/users/droberts/drober~1.htm



=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

RE: biostatistics careers

[Seymann, Richard]

And if I may muddy the waters even more, what is the difference between
biostatistics and biometry?
Dick
___
Richard G. Seymann, Ph.D. 
Professor of Statistics 
Director of Academic Assessment
Director of the Westover Honors Program
Lynchburg College, Lynchburg, VA 24501
Phone: (804)544-8258, Fax: (804)544-8658




-Original Message-
From: Rich Ulrich [mailto:[EMAIL PROTECTED]]
Sent: Monday, November 19, 2001 11:58 AM
To: [EMAIL PROTECTED]
Subject: Re: biostatistics careers


On Mon, 19 Nov 2001 08:07:33 -0500, Bruce Weaver
<[EMAIL PROTECTED]> wrote:

> 
> On Sun, 18 Nov 2001, Stan Brown wrote:
> 
> > What _is_ "biostatistics", anyway? A student asked me, and I
> > realized I have only a vague idea.
> 
> 
> There was a thread on "biostatistics versus statistics" a couple years
> ago, I think, but I was unable to find it at google groups.  Maybe someone
> out there saved some of it.

groups.google.com  on < biostatistics statistics > 
 - I found a couple of notes, within the top 100.  
There were several comments on 23 Feb 2000  
with the subject line, "re:biostatistics".  They mention
that medical background is important.  And vocabulary.

Also, as I vaguely remembered, I personally had answered a 
similar question, on 18 Feb 1998:

=== from my 1998 comment:
 - There are a couple of dozen or so U.S. universities that include
a "Graduate School of Public Health."  Here at the University of
Pittsburgh, it is the GSPH  that awards a degree in biostatistics.

The course work for the degree does include courses which would not
be required for "statistics" as I imagine it -  epidemiology (chronic
vs  acute diseases), vital statistics, health services administration.
[ ... ]
=== end of 1998 citation

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


=
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/
=

Maximized lambda4

[Wuensch, Karl L]

Callender and Osburn (Educational and Psychological Measurement,
1977, 37, 819-825) developed a method for estimating maximized lambda4, the
greatest split-half reliability coefficient among all possible split halves
for a scale.  The method is quite tedious to do by hand, and the authors
provided a FORTRAN program for accomplishing it.  Not having a FORTRAN
compiler, I'm considering writing an SAS program (IML) to do this, but don't
want to waste my time reinventing the wheel if someone else has already
written an SAS or SPSS program for this purpose.  If you are aware of any
such program, please advise me.  Thanks.

By the way, Callender and Osburn's work indicates that maximized
lambda4 is a much better estimate of a test's true reliability than is
lambda3 (coefficient alpha).


 ~~~  
Karl L. Wuensch, Department of Psychology,
East Carolina University, Greenville NC  27858-4353
Voice:  252-328-4102 Fax:  252-328-6283
mailto:[EMAIL PROTECTED]  
http://core.ecu.edu/psyc/wuenschk/klw.htm
 



=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: biostatistics careers

[Rich Ulrich]

On Mon, 19 Nov 2001 08:07:33 -0500, Bruce Weaver
<[EMAIL PROTECTED]> wrote:

> 
> On Sun, 18 Nov 2001, Stan Brown wrote:
> 
> > What _is_ "biostatistics", anyway? A student asked me, and I
> > realized I have only a vague idea.
> 
> 
> There was a thread on "biostatistics versus statistics" a couple years
> ago, I think, but I was unable to find it at google groups.  Maybe someone
> out there saved some of it.

groups.google.com  on < biostatistics statistics > 
 - I found a couple of notes, within the top 100.  
There were several comments on 23 Feb 2000  
with the subject line, "re:biostatistics".  They mention
that medical background is important.  And vocabulary.

Also, as I vaguely remembered, I personally had answered a 
similar question, on 18 Feb 1998:

=== from my 1998 comment:
 - There are a couple of dozen or so U.S. universities that include
a "Graduate School of Public Health."  Here at the University of
Pittsburgh, it is the GSPH  that awards a degree in biostatistics.

The course work for the degree does include courses which would not
be required for "statistics" as I imagine it -  epidemiology (chronic
vs  acute diseases), vital statistics, health services administration.
[ ... ]
=== end of 1998 citation

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


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: Evaluating students

[Eric Bohlman]

John Kane <[EMAIL PROTECTED]> wrote:
> Dennis Roberts wrote:

>> At 08:56 AM 11/16/01 -0700, Roy St Laurent wrote:
>> >It's not clear to me whether recent posters are serious about these
>> >examples, but
>> >I will reiterate my previous post:
>> >
>> >For most mathematics / statistics examinations, the "answer" to a
>> >question is the
>> >*process* by which the student obtains the incidental final number or
>> >result.
>> >The result itself is most often just not that important to evaluating
>> >students'
>> >understanding or knowledge of the subject.  And therefore an unsupported
>> >
>> >or lucky answer is worth nothing.
>>
>> the problems with the above are twofold:
>>
>> 1. this assumes that correct answers are NOT important ... (which believe
>> me if you are getting change from a cashier, etc. etc. ... ARE ... we just
>> cannot say that knowing the process but not being able to come up with a
>> correct answer ... = good performance)

No it doesn't.  It doesn't assume that they're not necessary, merely that
they're not sufficient.  To take it to the extreme, would you say a
student should get at least partial credit for a correct answer if he
arrived at it by copying it from another student's paper?  After all, 
he/she *did* answer correctly.



=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: biostatistics careers

[A.J. Rossini]

> "DR" == Dennis Roberts <[EMAIL PROTECTED]> writes:

DR> At 03:08 PM 11/19/01 +, A.J. Rossini wrote:
>> > "BW" == Bruce Weaver <[EMAIL PROTECTED]>
>> writes:
>> 
BW> On Sun, 18 Nov 2001, Stan Brown wrote:
>> >> What _is_ "biostatistics", anyway? A student asked me, and I
>> >> realized I have only a vague idea.
>> 
>> 
BW> There was a thread on "biostatistics versus statistics" a
BW> couple years ago, I think, but I was unable to find it at
BW> google groups.  Maybe someone out there saved some of it.
>> 
>> 
>> But it's much easier than that.  Biostatistics is simply
>> statistics (design, descriptive, and inferential) applied to
>> medical, basic biology, and public health problems.

DR> well, one difference in bio stat is a strong emphasis on
DR> probability sorts of problems ...

Hah!  So you think...




-- 
A.J. RossiniRsrch. Asst. Prof. of Biostatistics
U. of Washington Biostatistics  [EMAIL PROTECTED]
FHCRC/SCHARP/HIV Vaccine Trials Net [EMAIL PROTECTED]
-- http://software.biostat.washington.edu/ --
FHCRC: M-W: 206-667-7025 (fax=4812)|Voicemail is pretty sketchy/use Email
UW:   T-Th: 206-543-1044 (fax=3286)|Change last 4 digits of phone to FAX
Rosen: (Mullins' Lab) Fridays, and I'm unreachable except by email.


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: biostatistics careers

[Dennis Roberts]

At 03:08 PM 11/19/01 +, A.J. Rossini wrote:
> > "BW" == Bruce Weaver <[EMAIL PROTECTED]> writes:
>
> BW> On Sun, 18 Nov 2001, Stan Brown wrote:
>
> >> What _is_ "biostatistics", anyway? A student asked me, and I
> >> realized I have only a vague idea.
>
>
> BW> There was a thread on "biostatistics versus statistics" a
> BW> couple years ago, I think, but I was unable to find it at
> BW> google groups.  Maybe someone out there saved some of it.
>
>
>But it's much easier than that.  Biostatistics is simply statistics
>(design, descriptive, and inferential) applied to medical, basic
>biology, and public health problems.

well, one difference in bio stat is a strong emphasis on probability sorts 
of problems ...


_
dennis roberts, educational psychology, penn state university
208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED]
http://roberts.ed.psu.edu/users/droberts/drober~1.htm



=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Re: biostatistics careers

[A.J. Rossini]

> "BW" == Bruce Weaver <[EMAIL PROTECTED]> writes:

BW> On Sun, 18 Nov 2001, Stan Brown wrote:

>> What _is_ "biostatistics", anyway? A student asked me, and I
>> realized I have only a vague idea.


BW> There was a thread on "biostatistics versus statistics" a
BW> couple years ago, I think, but I was unable to find it at
BW> google groups.  Maybe someone out there saved some of it.


But it's much easier than that.  Biostatistics is simply statistics
(design, descriptive, and inferential) applied to medical, basic
biology, and public health problems.

So while a decent biostatistician need only concern themselves with
knowing all of statistics (which of course requires knowledge of most
of computer science and mathematics), as well as one or two of the
above scientific areas, a truly good one will know most science and
study related to medicine (which of course should include
biochemistry, economics, clinical trials, etc).

I'm only being slightly facetious.  I've come across the need to know
parts of nearly all of the areas mentioned above in my work, both to
communicate with as well as handle data analyses appropriately for
clients and colleagues.

best,
-tony

-- 
A.J. RossiniRsrch. Asst. Prof. of Biostatistics
U. of Washington Biostatistics  [EMAIL PROTECTED]
FHCRC/SCHARP/HIV Vaccine Trials Net [EMAIL PROTECTED]
-- http://software.biostat.washington.edu/ --
FHCRC: M-W: 206-667-7025 (fax=4812)|Voicemail is pretty sketchy/use Email
UW:   T-Th: 206-543-1044 (fax=3286)|Change last 4 digits of phone to FAX
Rosen: (Mullins' Lab) Fridays, and I'm unreachable except by email.


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

part. SS

[Dennis Roberts]

i have put up a little worked out example of the partitioning of SS in a 
simple 3 group situation ... for ANOVA ... with a diagram of where the 
components come from ...

http://roberts.ed.psu.edu/users/droberts/introstat/sspart1.png

this might be helpful to some ...

if you want to print ... you should do it in the landscape (horizontal) mode

_
dennis roberts, educational psychology, penn state university
208 cedar, AC 8148632401, mailto:[EMAIL PROTECTED]
http://roberts.ed.psu.edu/users/droberts/drober~1.htm



=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=

Categorical independents and continuous (counts) dependent

[Anna]

I am working on a dataset, which involves three categorical (two
dichotomies, and one of 5 categories) independent variables and a continuous
variable that consists of counts. The idea is to look at the significance of
the group differences/ the (main and interaction) effects of the
independents on the dependent. The problem is that a) some groups formed by
the independents are not at all equal in sample size (1 group has no people
left inside), and b) the dependent variable is not normally distributed and
has extreme outliers, which as part of the project should not be deleted. So
far, I have tried factorial ANOVA (though violating most of its
assumptions), Hierarchical LogLinear analysis, and multiple regression with
the independents entered as dummies. However, none of the above tests seem
appropriate. Any suggestions? Thank you ~ Anna


=
Instructions for joining and leaving this list and remarks about
the problem of INAPPROPRIATE MESSAGES are available at
  http://jse.stat.ncsu.edu/
=