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Date:         Wed, 30 Mar 2011 16:43:35 -0700
Reply-To:     Bridgette Portman <bportman@uci.edu>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Bridgette Portman <bportman@uci.edu>
Subject:      Re: exact versus asymptotic p-value under normal circumstances
Comments: To: "Marta García-Granero"
          <mgarciagranero@gmail.com>
In-Reply-To:  <4D91E85C.6090803@gmail.com>
Content-Type: text/plain;charset=iso-8859-1

Hi Marta,

No, I'm definitely reading the exact p-value. I find this strange too -- I've spent the last couple days searching the internet for an answer to this and I can't figure it out. My exact p-values on any table larger than 2x2 are almost invariably smaller than my asymptotic ones. I'm no longer trusting the exact values, which leaves me unsure how to analyze the results from tables larger than 2x2 when cell counts are low.

Has anyone used the SPSS exact tests module too? I am really stuck at this point.

Bridgette

> El 28/03/2011 22:34, Bridgette Portman wrote: > >> For example: On the crosstabs I just ran, X2=4.49, 3 degrees of >> freedom, >> asymptotic sig is showing up as .212, and exact sig as .028. All >> expected >> cell counts were greater than 5. > > Hi Bridgette: > > In my experience, exact p values are usually higher than their > asymptotic counterparts,(and both are very similar when sample sizes are > big). Therefore, I find strange the great discrepancy between the exact > & asymptotic p values that you report. Is there any chance that by > mistake you annotated the "Point probability" instead of the "Exact sig. > (2-tailed)"? > > Best regards, > Marta GG > > ===================== > To manage your subscription to SPSSX-L, send a message to > LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the command > INFO REFCARD > >

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