# When to use robust standard errors in Poisson regression?

I am using a Poisson regression model for count data and am wondering whether there are reasons not to use the robust standard error for the parameter estimates? I am particularly concerned as some of my estimates without robust are not significant (e.g., p=0.13) but with robust are significant (p<0.01).

In SAS this is available by using the repeated statement in proc genmod (e.g., repeated subject=patid;). I've been using http://www.ats.ucla.edu/stat/sas/dae/poissonreg.htm as an example which cites a paper by Cameron and Trivedi (2009) in support of using robust standard errors.

-