Sample Size and Logit Models

["Walter R. Paczkowski" <dataanalytics@earthlink.net>]

Hi,

I'm hoping someone has some insight about sample size and logit
estimation that could help me.  I inherited a logit model from a
client in the direct marketing area.  The previous consultant used
approximately 143,800 observations in the training data set, of which
only 50 (0.03%) were the target ( = 1) value for the dependent
variable.  The literature I could find gives very little guidance on
sample sizes (Hosmer & Lemeshow have some material, but they
basically say that little has been done).  Does anyone know of some
literature or even rules-of-thumb about sample sizes and/or ratio of
target to non-target values of the dependent variable?  The use of
143,800 observations is excessive.  Does this do anything to the
significance of the estimates (e.g., am I always guaranteed very small
p-values?)?  Is oversampling of the target value the key and if so,
how do I calculate weights for the estimations?  

Any guidance or suggestions in this area are definitely welcome.

Walt Paczkowski

_________________________________

Walter R. Paczkowski, Ph.D.
Data Analytics Corp.
44 Hamilton Lane
Plainsboro, NJ  08536
(V) 609-936-8999
(F) 609-936-3733