Dear STATALISTers,

I would like to ask your help on an issue I´ve come across in terms of an interaction term, or rather how to interpret:
Specifically, I am running a multivariable logistic regression model (outcome: procedural efficacy of a procedure/surgery) in order to study the impact of a medication (finasterid) on the procedure (prostate enucleation). Overall, finasterid has a positive effect (see A). Next I want to see if the effect of finasterid is modulated by prostate size (variable: pvolquart). In the regression output (see B), the interaction term is significant for the 4th volume quartile of prostate size (which I interpret as: the overall positive impact of the medication is driven by its effect on prostates of the 4th volume quartile, while there is no positive effect in the 1-3rd volume quartile).
However, when I want to confirm the positive interaction via the testparm command (see C), it is no longer significant. Is testparm the incorrect test in this case, or does it mean that there is no significant interaction?

Your help is greatly appreciated!



A)

Array


B)

Array




C)

Array