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Topic: F-test for comparing variances?
Replies: 4   Last Post: Nov 10, 2006 1:04 AM

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Richard Ulrich

Posts: 2,858
Registered: 12/13/04
Re: F-test for comparing variances?
Posted: Nov 8, 2006 11:01 PM
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On 8 Nov 2006 11:08:22 -0800, "Reef Fish"
<large_nassua_grouper@yahoo.com> wrote:

>
> Richard Ulrich wrote:

> > On 5 Nov 2006 17:55:46 -0800, "Reef Fish"
> > <large_nassua_grouper@yahoo.com> wrote:

> > >
[snip]

RU > >
> > umm. You still need to get a test value, subtract, then double....
> > which I described usefully. Bob was not paying attention, too eager
> > to criticize.

RF >
> WRONG, WRONG, WRONG.
>
> 1. For testing with a given alpha, such as a two-tailed test with F,
> you find F(.025) and F(.975) before you get the test value,
> because
> you DON'T have to see if the numerator is greater or smaller. You
> KNOW the degrees of freedom of the F.


I can apologize, and clarify.

No doubt I confused Bob by saying "test value" instead
of saying "two-tailed p-value."

If you want a two-tailed p-value -- which is the modern
standard, instead of simply 'flagging' the test result --
you need to double the smaller extreme.

Here are a *couple* of conventions -- presenting p-values;
and doubling a one-tailed value to get a two-tailed value.

[snip]

RU >
> > By now, he should recognize that he *often* does not understand
> > what's being said. Why else is it, that every 'fight' in the stat
> > groups features Bob?

RF >
> Everytime you say I don't understand, it's always because I was at
> several steps AHEAD of you and understand every word of yours to
> be ERRORS resulting from your lack of education.


Your next step, Bob, is to consider how to compute the "p-value",
which everyone wants these days. Catch up.


[snip]
>
> You REMAIN ignorant, and a malpracticing Quack, Richard Ulrich.


That remains absurd. Stream-of-consciousness garbage.

>
> That may be an insult you deserve -- but hardly gratuitous!


Yes. Gratuitous. Nobody asks for this, and 10,000 readers do
not want to see it. *If* I were so obviously 'ignorant', nobody
would *need* Reef Fish Bob Ling to belabor the point.

The only 'end' that it seems to serve is an ongoing intention
to bully and intimidate. Bad net-citizenship.


--
Rich Ulrich, wpilib@pitt.edu
http://www.pitt.edu/~wpilib/index.html



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