I'm trying to look at the significance of a covariate through a drop in deviance test of two Poisson models. For example, mod1 might have 4 covariates, mod2 would have the same 4 covariates plus one more of particular interest. I've calculated the model deviance and df for each model with:
# vector of individual deviance residuals
#sum of squared deviance residuals = model deviance
And the df for each model I calculated as the number of observations minus the number of parameters.
Is it correct to then use:
to find the p-value of my additional covariate?
I'm sure there are commands for this in R, however I'm using a program that won't let me use the normal regression-based packages, so I have to do things long-hand. Any corrections, affirmations, or advice would be much appreciated!
Thanks very much for your time,
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