A new Pew study of religion and class shows an almost direct line between education and income. The denominations with the highest average income - Reform Jews, Hindus, and Conservative Jews - also have the highest level of education. Two-thirds of Reform Jewish households make more than $75,000 per year. The median income of a household of four is $50,000.
David Leonhardt, in the New York Times article on this study, rightly notes the education/income link. He wonders why the secularists and Unitarians, who have high levels of education, do not have household incomes to match.
I have a hypothesis: secularists and Unitarians have a high unmarried rate. Secularists tend to be younger than other religious groups, and less likely to have married yet. Unitarians have a high fraction who changed religions, often after a divorce. Both of these conditions reduce household income compared to other religious groups, which are more married.