|Date: ||Tue, 6 Dec 2005 10:59:57 -0800|
|Reply-To: ||David L Cassell <davidlcassell@MSN.COM>|
|Sender: ||"SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>|
|From: ||David L Cassell <davidlcassell@MSN.COM>|
|Subject: ||Re: PROC LOGISTIC: Odds ratios with interactions|
|Content-Type: ||text/plain; format=flowed|
Jay replied (to my comment):
>Well it depends on the size of the effect doesn't it?
Yes. I should have been clearer. If the interactions are minute but
statistically significant, then their effect on the main effects may be so
small that odds ratios of A computed at each level of B could be
> In a large
>dataset even a tiny interaction can be statistically significant, in
>which case interpretation of main effects might still make good sense.
Yes. Unfortunately, with large enough data sets, one can get *everything*
to be statistically significant. Even when the paramter estimates are so
that they have no scientific or business-case meaning.
>I've recently completed logistic regression analyses of tens of
>thousands of medical records in which virtually every minuscule 3- &
>4-way interaction was significant at the .001 level.
Ugh. You have my deepest sympathies. :-) :-)
David L. Cassell
3115 NW Norwood Pl.
Corvallis OR 97330
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