Stereotypically, people say that religion is the "opiate of the masses", and expect poor people to be religious, because it gives them solace for their problems.
But most of the religious people I've known are relatively wealthy, Mercedes-driving people, to whom Christianity gives the comfort of believing that their wealth is the result of God's plan, and of their own virtue, rather than accident.
And the people in-between rich and poor tend to deviate less from accepted social behavior, and thus are more likely to be religious.
So every possible economic status increases the priors of being religious. Wait, that can't be right.