I am fitting a gamma GLM on insurance claims predicting severity. Using log( claim count) as offset and ultimate claim amount as target variable and a gamma error structure. Model converges but Actual / Predicted claim amount does not converge to 100% in the modeling data. Per my understanding, when a GLM converges the within sample model prediction is always 100%. Am I missing something here?
I also tried using an intercept only model expecting 100% A/ E on overall level but still unable get it. Is it some additional arguments I need to provide, or is gamma not a good fit. I then went to lognormal fit but with not much success