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st: Converting an odds ratio in a risk ratio - Logit


From   "Leda Inga" <ledainga@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Converting an odds ratio in a risk ratio - Logit
Date   Sat, 14 Jun 2008 19:54:22 -0500

Dear statalisters:


I ran a logit with diferent dummies as you can see below:

Y = f(X, D1_3, D4, D5, .., D10, D_more10)

X: set of regressors

D_: dummies that classify each indiviual by the number of visits made
to the doctor.

Since I ran a fixed effect logit, I only can get the odds ratio of
each dummy. Nevertheless, I would like to convert them in risk ratios.
I hope that someone has any idea or has been in a similar situation
before.

According to the recomendation of Jun Zhang and Kai F. Yu
(http://jama.ama-assn.org/cgi/content/full/280/19/1690#ACK) it can be
used the following:

RR= OR/ (1 - Po + Po*OR)

where Po is the incidence of Y in the "unexposed group".

Since I used diferent dummies, I'm not sure what should be my
"unexposed group" for each dummy. I know that the coefficient of each
dummy must be interpreted versus the reference group (in my case, zero
visits). But maybe to get the risk ratios of "X" visits versus the
reference (zero visits) the unexposed group should be "X-1" visits or
all but "X" (since each dummy takes values of zero for all individuals
who didn't have "X" visits)

Any help would be really appreciated.
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