Hello,
I need help interpreting the main effects in a Poisson model with a binary covariate, a continuous covariate and their interaction. I'm using STATA 13 for Windows.
My understanding is that, in general, the estimate corresponding to a main effect in such a model only applies to the baseline values of the other main effect. For instance, if there is a binary covariate for sex and a binary covariate for employment, then in a model with sex, employment and the sex-by-employment interaction, the main effect of sex only applies to those subjects who have a value of zero for the employment variable. Similarly, the main effect of employment only applies to those subjects who have a value of zero for the sex variable. When interpreting such a model, I can verify that this is true by running other models within strata of the covariates and compare the stratum-specific estimates to the main effects of the interaction model.
When one of the covariates is continuous, the main effect of the continuous covariate is still the same as what is produced by a model restricted to the subjects with the baseline value of the binary covariate. However, I'm not sure how to interpret the main effect of the binary covariate. Any guidance would be most appreciated.
Thanks
I need help interpreting the main effects in a Poisson model with a binary covariate, a continuous covariate and their interaction. I'm using STATA 13 for Windows.
My understanding is that, in general, the estimate corresponding to a main effect in such a model only applies to the baseline values of the other main effect. For instance, if there is a binary covariate for sex and a binary covariate for employment, then in a model with sex, employment and the sex-by-employment interaction, the main effect of sex only applies to those subjects who have a value of zero for the employment variable. Similarly, the main effect of employment only applies to those subjects who have a value of zero for the sex variable. When interpreting such a model, I can verify that this is true by running other models within strata of the covariates and compare the stratum-specific estimates to the main effects of the interaction model.
When one of the covariates is continuous, the main effect of the continuous covariate is still the same as what is produced by a model restricted to the subjects with the baseline value of the binary covariate. However, I'm not sure how to interpret the main effect of the binary covariate. Any guidance would be most appreciated.
Thanks
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