A new Washington Post-ABC News poll last week showed support for gay marriage hitting an all-time high at 58 percent, with support having risen by 21 points over the last decade alone.

But some social conservatives say polls like this one are wrong, and that they over-sell the actual amount of support for gay marriage. …

So are they right? Are the polls often wrong?

In a word, yes — at least to some degree. Polls on gay marriage ballot initiatives generally under-estimate the opposition to gay marriage by about seven percentage points, according to a 2010 study by New York University political science professor Patrick J. Egan.

“The share of voters in pre‐election surveys saying they will vote to ban same‐sex marriage is typically seven percentage points lower than the actual vote on election day,” Egan wrote. He also noted, however, that polls are generally accurate when it comes to the percentage of people supporting gay marriage.