Date:         Mon, 29 Jul 1996 14:54:29 +0100
Reply-To:     John Whittington <johnw@MAG-NET.CO.UK>
Sender:       "SAS(r) Discussion" <SAS-L@UGA.CC.UGA.EDU>
From:         John Whittington <johnw@MAG-NET.CO.UK>
Subject:      Re: Whoops! Re: CHI-SQUARE goodness-of-fit in easy form ??
Comments: To: SFBAY0001 <sfbay0001@aol.com>

On Thu, 25 Jul 1996, SFBAY0001 <sfbay0001@aol.com> wrote:
 
>If I am not mistaken, the EXACT test supported in PROC FREQ uses the
>hypergeometric probability distribution, NOT the chi-square distribution.
>It is sometimes referred to as "Fisher's Exact Test for a 2 by 2 table".
 
I'm getting slightly confused here.  An 'exact' test is surely precisely
what it says - it is a statement of the exact probability of getting a table
'as extreme as' the one observed, given the marginal totals that one has.
As such, there is no need to refer to any theoretical distribution - one
(the computer!) simply counts up two lists of possibilities and divides one
by the other.  Anything less than that may be a good *approximation* to an
'exact' method, but is not strictly '#exact'.
 
.. that's how I see it, anyway.
 
John
 
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