Thread View: sci.math.stat
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Started by an7855
Sat, 23 Jan 1993 20:41
Re: F distribution and relation to Beta
Author: an7855
Date: Sat, 23 Jan 1993 20:41
Date: Sat, 23 Jan 1993 20:41
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3774 bytes
>
> pddxt@chalk.cpceng.cpc.gmeds.com (Dino Triantos 575-4386) writes:
>
> >I'm working on a problem in Mood, Graybill and Boes that asks to find the
> >relationship between the F and Beta distributions. The problem asks: If
> >X has an F distribution with m and n degrees of freedom, show that
> >
> > mX/n
> > W = ------- has a Beta distribution.
> > 1 + mX/n
>
> >Any suggestions or solutions would be greatly appreciated!
>
> >Dinos Triantos
> >GM/Midsize Automotive Division
> >Vehicle Systems Analysis
> >C-P-C Engr. Center Rm# G241
> >Fax: (313) 575-7270
> >E-mail: pddxt@cpceng.cpc.gmeds.com
>
> Is this a homework problem or will the solution to this
> statistical issue help GM build better cars? The net has
> informal prohibitions against providing answers to homework
> problems. The problem you raise is a very standard homework
> assignment in undergraduate statistics classes. When I did it as
> a homework problem many years ago I remember that it was a bit
> easier to do it as W = 1/(1+(m/n)F). It won't help you solve it,
> but a useful insight is that W is often known as R^2. Good luck!
>
What rock did this respondent crawl out from under of?
[I've carefully removed his identity from his response.
I'm more concerned with what he represent that who he is.]
Here we have an individual working in industry who has a statistics
question and some clown decides to disgrace the profession by going beyond
even stereotypical behavior to insult the client (Is this a homework
problem or will the solution to this statistical issue help GM build
better cars?) and provide some helpful misinformation (When I did it as a
homework problem many years ago I remember that it was a bit easier to do
it as W = 1/(1+(m/n)F). Put the two together and you've got intellectual
bullying (or incompentence, depending on the reason for the
misinformation) at its worst. And no one bothers to take the respondent
to task!
I've never posted to this group because of my anger at the amount of
abuse and misinformation that gets passed out. I've prefered to send my
advice by private e-mail and take part in a real dialogue with my
"clients". But I've just decided I have no further interest in even
lurking.
Wouldn't it have been nice if Mr. Triantos had learned that
statisticians were only too happy to help those who were eager and willing
to learn? Why not merely have told him
"The only trick to this problem is that there's no trick! It's
straightforward. Just find X in terms of W,
X = (n/m) (W/(1-W)), and don't forget the Jacobian!
Also, check the region over which the density is positive. It's trivial
here but it's important, especially in more than one dimension where even
"great men" have screwed up calculating marginal densities by using the
wrong limits of integration."
Of course, it's too late to tell him now. If I were he, I'd be
long gone. As it is, *I'm* gone after this posting.
-------------------------------------------------------------------------
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Re: F distribution and relation to Beta
Author: Gary McClelland
Date: Sat, 23 Jan 1993 23:43
Date: Sat, 23 Jan 1993 23:43
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an7855@anon.penet.fi writes:
>>
>> pddxt@chalk.cpceng.cpc.gmeds.com (Dino Triantos 575-4386) writes:
>>
>> >I'm working on a problem in Mood, Graybill and Boes that asks to find the
>> >relationship between the F and Beta distributions. The problem asks: If
>> >X has an F distribution with m and n degrees of freedom, show that
>> >
>> > mX/n
>> > W = ------- has a Beta distribution.
>> > 1 + mX/n
>>
>> >Any suggestions or solutions would be greatly appreciated!
>>
>> >Dinos Triantos
>> >GM/Midsize Automotive Division
>> >Vehicle Systems Analysis
>> >C-P-C Engr. Center Rm# G241
>> >Fax: (313) 575-7270
>> >E-mail: pddxt@cpceng.cpc.gmeds.com
>>
>> Is this a homework problem or will the solution to this
>> statistical issue help GM build better cars? The net has
>> informal prohibitions against providing answers to homework
>> problems. The problem you raise is a very standard homework
>> assignment in undergraduate statistics classes. When I did it as
>> a homework problem many years ago I remember that it was a bit
>> easier to do it as W = 1/(1+(m/n)F). It won't help you solve it,
>> but a useful insight is that W is often known as R^2. Good luck!
>>
> What rock did this respondent crawl out from under of?
> [I've carefully removed his identity from his response.
>I'm more concerned with what he represent that who he is.]
Then I'll carefully put the identity back in. My name is Gary
McClelland and I'm a professor at the Univ of Colorado. Who may
I ask is an7855@anon.penet.fi? Do you have the courage of your
convictions Mr. or Ms. Anon?
> Here we have an individual working in industry who has a statistics
>question and some clown decides to disgrace the profession by going beyond
>even stereotypical behavior to insult the client (Is this a homework
>problem or will the solution to this statistical issue help GM build
>better cars?)
As a professor, I do not think it appropriate for the net to
provide students with answers to homework problems. The original
poster indicated that it was a problem from a standard
statistical textbook. It appears in all respects to be a
homework problem. The same poster posted a similar note asking
about a different homework-like problem within the week. Perhaps
I goofed in inferring from so little data that a trend was
developing, but I thought it appropriate to suggest that if this
were homework, that responses from the net would not be
appropriate. But perhaps I'm wrong on net opinion. Should we
take a vote as to whether we should be answering homework
problems?
I've also served as consultalnt for the General Motors Research
Labs. I know that they have some _very_ competent statisticians.
If the poster needs help with work-related statistical issues,
then there are better places within GM to seek answers to those
questions rather than appealing to the net.
> Put the two together and you've got intellectual
>bullying (or incompentence, depending on the reason for the
>misinformation) at its worst. And no one bothers to take the respondent
>to task!
At least no one not willing to hide behind an anonymous name and
address...
> I've never posted to this group because of my anger at the amount of
>abuse and misinformation that gets passed out. I've prefered to send my
>advice by private e-mail and take part in a real dialogue with my
>"clients".
One nice thing about postings to the net, as opposed to private
e-mail, is that postings are subject to a form of peer review.
> Wouldn't it have been nice if Mr. Triantos had learned that
>statisticians were only too happy to help those who were eager and willing
>to learn?
There is a lot of evidence that suggests that students will learn
and retain better problems that they solve on their own as
opposed to having someone else solve the problems for them.
>-------------------------------------------------------------------------
>To find out more about the anon service, send mail to help@anon.penet.fi.
>Due to the double-blind system, any replies to this message will be anonymized,
>and an anonymous id will be allocated automatically. You have been warned.
Maybe anonymous postings are useful for some of the lurid alt.*
newsgroups, but do we really need to hide behind anonymous IDs
for sci.math.stat?
gary mcclelland
univ of colorado
mcclella@yertle.colorado.edu
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