Logit software

Bob Wheeler bwheeler at ssnet.com
Fri Aug 12 16:36:54 EST 1994

> I'm sorrry that this posting earlier got truncated.  What I would like to
> find is a PC based program for carrying out Logit transformations.  I
> assume this might be part of a more extensive package of statistical
> routines, but an inexpensive stand alone program would be fine too.  Also
> any information about the use of this plot and/or pitfalls would be
> appreciated.  
> Phil Carl

Several statistical packages do logisic analysis if this is what you
want, and not just a simple transformation to a logit.  A logit is
defined as m=log(p/1-p) where 0<=0<1. Logistitc analysis tries to fit
a linear model, say a+bx, to m, which means that the fitted value,
p=e^m/(1+e^m) ranges between 0 and 1.  The fitting is iterative, since
there is no closed algorithm for the problem.  Sorry about the verbosity,
but I wanted to maker sure we were on the same wavelength.

SAS, of course does logistic analysis, as does SPSS, and ECHIP.  The
original program, and a very satistfactory one it still is, is GLIM
from NAG.  (Note ECHIP is an experimental design and analysis program,
and not a general purpose statistical program as are the others.)

	Bob Wheeler, ECHIP, Inc.

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