Lord Parkin
aka emperor
Heh... although actually I don't mind Great Prophets. Even if you don't have a good shrine to build, in the early game they're good for +2 hammers and +5 commerce in your capital (+3 beakers as well with Representation), and in the later game they're great for Golden Ages. Plus occasionally it can be useful to bulb a tech, like Theology or Divine Right. Not too shabby really.Try looking in your city each turn, mouse over the GP slider bar, you will see the changes over several turns , it soon becomes apparent how it works
your most Likely get a prohet. "MURPHY'S LAW"- if something can go wrong -IT WILL

By the way, to the original poster, there is an article HERE which explains how Great Person probabilities are calculated. However, it's quite old and I'm not completely sure it still applies with the latest patch for BTS - but it should at least be similar, if not exactly the same.