[Rd] Application of step to coxph using method="exact" (PR#6646)

kolassa at stat.rutgers.edu kolassa at stat.rutgers.edu
Thu Mar 4 18:14:52 MET 2004

Full_Name: John E. Kolassa
Version: Version 1.8.1
OS: Solaris
Submission from: (NULL) (

Stepwise model selection for coxph appears to fail with method="exact".
The code


produces the error message 

Start:  AIC= 733.07 
 Surv(1:100, rep(1, 100)) ~ factor(rep(1:4, 25)) 

Error in "[<-"(`*tmp*`, i + 1, , value = extractAIC(nfit, scale, k = k,  : 
        number of items to replace is not a multiple of replacement length

The same code without specifying method 

runs through, and gives what looks like a reasonable answer.  Thanks, John

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