Most national pollsters are still using samples of registered voters rather than “likely” voters and some suggest that Mitt Romney will have an advantage when this change is made but Mark Blumenthal suggests it’s too early.
“In almost every election dating back to 1980, the margins separating the top candidates in horse race polls shifted significantly after the party conventions. Only in 1996 did those margins remain roughly the same throughout the year. In other years, the shifts in voter preferences that occurred after the party conventions, shifts that have benefited both Democratic and Republican candidates, would have overwhelmed the relatively modest differences that earlier likely voter screens would have produced.”
“In the end, if all pollsters applied likely voter screens right now, Romney’s numbers would be slightly better, but there is a long way to go before any horse race poll should be considered an accurate forecast of the outcome.”