Potential

It is well know that there is pretty good data showing that American Protestant Christians do not come close, on average, to tithing. (Furthermore, there is a general result that denominations whose members have higher incomes actually do worse). Doug and I have wondered if there was a measure of the unrealized potential for social compassion from this gap in giving. Anthony Bradley, at Resurgence, claims to have such a number: $143 billion dollars for all American Christians. Unfortunately, Mr. Bradley doesn't give a source, but the figure looks to me to be just over one percent of GDP. (His assertion that one percent of GDP is 25 billion appears to me to be just wrong ---I wonder if he means one percent of the federal budget).

Has anybody seen specific sources for a number like this? $143 billion seems entirely plausible to me.