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Re: st: ST: logistic regression and 'adequate numbers'

From   Maarten buis <>
Subject   Re: st: ST: logistic regression and 'adequate numbers'
Date   Wed, 6 Apr 2011 09:06:29 +0100 (BST)

--- On Wed, 6/4/11, Ronald McDowell wrote:
> I'm modelling the log odds of a
> binary outcome as function of several covariates including
> age. Unsurprisingly as my sample gets older I have fewer
> numbers samppled for each year of age, and was wondering if
> anyone had come across or used a 'rule of thumb' in terms of
> how many sampled per age was 'too few' to include in the
> model? I've read of studies restricted to certain ages
> because of 'inadequate numbers' but haven't found a
> definition of the latter.
> I'm aware I can perform sensitivity analysis, look at
> residuals and the usual diagnostics (not all of which are
> available in STATA in this case unfortunately), but if
> anyone had any thoughts on the matter I'd be interested.

There is a fairly complete set of types of residuals and other
diagnostic tools after you estimate your model with -glm-.
When it comes to age, I would not be worried about the number
of observations but about selective mortality: people who 
survive to a very old age are different from the general 
population in many ways.

Hope this helps,

Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen

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