Forget everything you ordinarily associate with religious study. Strip away all the reverence and the awe and the art and the philosophy of it. Treat the subject coldly. Imagine yourself to be a theologist, but a special kind of theologist, one who studies gods the way an entomologist studies insects. Take as your dataset the entirety of world mythology and treat it as a collection of field observations and statistics pertaining to a hypothetical species: the god. Proceed from there.