Carl Bialik's "The Numbers Guy" column in WSJ.
He cautions that the numbers are pure swag, since the census doesn't collect such info, so the surveys employed at a bit patchy. Compared to the rest of the world (70 nations do ask on the census), America has little sense as to the faith of its citizenry, says Bialik.
Important? He uses the example of the proposed lower Manhattan mosque. Experts say NYC has 600k Muslims, with some saying 600-800k in Manhattan alone! If anywhere near true, then the 1.3m estimate above is clearly wrong.
Some experts say the real Muslim number is above 2m and perhaps as high as 7m. Of course, there's the subset of who's really active, but that can be balanced by kids if the surveys focus only on adults, like above
Since the slide above only adds up to about 228m, I guess you can surmise that about 75m kids are absented, but because you can probably split those out similarly, then you arguably boost everybody's total by a quarter, so 72m Catholics, 3.4m Jews, 1.6m Muslims and so on.
But even on that basis, it seems weird that there are 5 Catholic Supreme Court justices and 4 Jews.
Other interesting factoid: if you add up the atheists, agnostics, refuseniks and other non-religious, and then plus in the extra quarter, you're talking upwards of 60m non-participants, or one-in-5 Americans. That seems high, based on other stuff I've seen, but about right when youth are pinged in surveys.