Date:         Tue, 27 May 2008 05:53:11 -0700
Reply-To:     martholt <martinholt42@YAHOO.CO.UK>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         martholt <martinholt42@YAHOO.CO.UK>
Organization: http://groups.google.com
Subject:      Number of events required
Comments: To: sas-l@uga.edu
Content-Type: text/plain; charset=ISO-8859-1

Hi,

I've always understood that, when doing logistic regression, at least
10 of the rarer events are required per variable to be entered into
the model. I've been reading "Categorical Data Analysis using the SAS
System" by Maura E. Stokes et al, a SAS Institute book I believe. Here
is written, "Your choice depends partially on the sample size. There
should be at least 5 observations for the rarer outcome per parameter
being considered in the expanded model. Some analysts would prefer at
least 10."

Does anyone have any information supporting the use of 5 ?

Best Wishes,

Martin Holt