st: predictions after clogit

[Ginger Smith Carls <smithga@umich.edu>]

Hello statlisters,

I would like to generate predictions after clogit.  For example, my  
dependent variable is a hospitalization.  I want to predict the number  
of fills of a specific drug in my sample under different scenarios.   
The diffent scenarios are defined by different values of an indepdent  
variable.  One scenario is at the sample mean.  The other is to add  
some amount to the variable.  What is the best way to do this?  Some  
of the options are:

a. predict outcome for diferent scenarios and calculate the difference
b. use mfx to calculate the marginal effect of the change

When I run mfx, it says there is no effect.  When I run predict, the  
predicted value is identical for each scenario.  I tried other predict  
options and the results did not make sense either.  One thing to note  
about my data is that more than one "yes" or 1 is allowed to occur  
within each group.  Most groups have only one success, but some have  
more than 1.

The reason I want to do this, rather than simply report the odds ratio  
for the variable of interest, is that the odds ratio may not  
approximate relative risk in my case because the outcome is relatively  
common.  I would like to report . when x var increases by 20 points,  
yvar increases by some percent.

It is my understanding that the odds ratio does not approximate  
relative risk unless the outcome is rare or in special designs that  
are not the case here.  I don't think my outcome is sufficiently rare  
to assume that odds ratio~= relative risk, so I am looking for an  
alternative way to report results.

Thanks for your help,
Ginger

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