I didn't see it in the study, but did they ever go back and see how many of the "Athiests" remained athiest.
Another thing to note is that the ASVAB would only test those athiests that intended to join the service. Since most of the athiests I knew had no intention of going off to war their ASVAB scores are unavailable. Getting their SAT scores would be awful difficult as well as they ended up dropping out of HS. An area the religious tend to be better at. Higher graduation rate. Seeing as how you have to graduate to join the service, the dumber of the athiests tend to get left off.
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." Thomas Jefferson