Date: Fri, 30 May 2008 09:01:53 -0500
Reply-To: Citam <citam.sasl@GMAIL.COM>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: Citam <citam.sasl@GMAIL.COM>
Subject: Re: Number of events required
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On 5/27/08, martholt <firstname.lastname@example.org> wrote:
> 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 ?
I would not go below 5. When pressed, I have used 5, but those two
particular analyses never saw the light of peer-reviewed publication.
Hopefully, you know enough about the science to support that model.
You could simulate the data to see what effects 5-10 observations have
on the estimates and their variance. Unless I had restrictions, I
would push hard to get at least 10 observations, but that cannot
Also, searching the archives you will find that we have discussed
this, but as it is a tricky issue, we will continue to discuss it...