human behavior is predicted based on where they live.
is the "based on" a preposition phrase here?
do i need a comma before "based"?
I wouldn't call it a prepositional phrase as 'based' is not the complement of the preposition. It's a bit of a mixed-up sentence, IMO, because you have 'they' and 'human behaviour'. I'd be tempted to change it to 'people's behaviour'. I don't think a comma is necessary there.