R help - May 2012 - anova.coxph for multiple events model

Hi,

I'm trying to do a multiple events model using coxph. I need to choose which
covariates stay in the final model and i'm using anova but it seems that it
doesn't work with robust variances as a error message appears when I try to
do it:

/PWPfit<-coxph(Surv(ini,fim,status)~Sexo+Transmissao+Regime+HAART+Drogas+Psi+
+ CD4+CV+Neo+IO+cluster(idPARTICIPANTE)+strata(Estrato),data=PWP)
> anova(PWPfit)
Error in anova.coxph(PWPfit) : 
  Can't do anova tables with robust variances
/

However when I fit two different nested models the function anova seems to
work:

/>
PWPfit<-coxph(Surv(ini,fim,status)~Sexo+Transmissao+Regime+HAART+Drogas+Psi+
+
CD4+CV+Neo+IO+cluster(idPARTICIPANTE)+strata(Estrato),data=PWP)
> 
>
PWPfit2<-coxph(Surv(ini,fim,status)~Sexo+Transmissao+Regime+HAART+Drogas+Psi+
+
CD4+CV+Neo+cluster(idPARTICIPANTE)+strata(Estrato),data=PWP)
> 
> anova(PWPfit,PWPfit2,test="Chisq")
Analysis of Deviance Table

Model 1: Surv(ini, fim, status) ~ Sexo + Transmissao + Regime + HAART + 
    Drogas + Psi + CD4 + CV + Neo + IO + cluster(idPARTICIPANTE) + 
    strata(Estrato)
Model 2: Surv(ini, fim, status) ~ Sexo + Transmissao + Regime + HAART + 
    Drogas + Psi + CD4 + CV + Neo + cluster(idPARTICIPANTE) + 
    strata(Estrato)
  Resid. Df Resid. Dev  Df Deviance P(>|Chi|)
1       371    1253.00                       
2       372    1253.30  -1    -0.31    0.5794
Warning message:
In all(lapply(object, function(x) inherits(x, "coxph"))) :
  coercing argument of type 'list' to logical

/

Does anyone know why this happens? Should I do it separately for each
variable or is there an alternative way to choose covariates in this kind of
models?

Thanks a lot,

Andreia Leite (Biostatistics Master Degree Student)
Faculdade de Ci?ncias, Lisbon, Portugal 

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