[R] stepwise selection for conditional logistic regression

[David Winsemius]

On Feb 22, 2012, at 12:03 AM, Subha P. T. wrote:

> Hi David
> My data set has about 20 significant variables and  step function  
> with logistic regression is working fine( in R-commander). I tried  
> to get conditional logistic by introducing the stratum variable and  
> clogit. The clogit is not converging but is giving the summary of  
> the model. When step/step AIC/..are used, the message given is  
> "ERROR: number of rows in use has changed".

Caveat: I do not generally use stepwise methods and I have no  
experience with this particular message. Nonetheless it suggests that  
you have some variable in the model tat differs from the others with  
respect to missingness. Have you tried using subset() or  
complete.cases() to select a set of non-missing data for all tested  
variables?

--
David Winsemius, MD
West Hartford, CT