Mark Blumenthal has the definitive takedown of Gallup's slightly skewed sample that undercounts non-white voters:
Instead of achieving the target of 12.1 percent black set by the March 2011 CPS, the average across the seven surveys was 11.3 percent black. Instead of hitting the CPS target of 13.7 percent Hispanic, the seven surveys averaged just 12.4 percent Hispanic.
It's a small difference – but when the race is close, a tangible one.
The Dish 