PPP Poll: 33% of Voters Say Gay Marriage Should be Legal, 57% Say It Should Be Illegal

Liberal blogger Nate Silver takes a look at a new poll on gay marriage conducted by the Democratic firm Public Policy Polling:

On the heels of a CNN poll earlier this week which was the first ever to show majority support for gay marriage, Public Policy Polling has come out with a survey showing a clear majority of their respondents still opposed to it: 57 percent of registered voters who responded to their survey think gay marriage should be illegal, and 33 say it should be legal. This contrasts sharply with CNN's results, which showed either a 52-46 majority in support of gay marriage or a narrow 48-50 plurality opposed to it, depending on the question wording. In fact, the 33 percent PPP shows in support of gay marriage is the lowest of any poll since 2006.

Silver runs through a number of reasons why CNN and PPP came up with such different results. CNN polled all adults, while PPP polled registered voters; CNN used live operators, while PPP used an automated recording to conduct the poll:

PPP's was, to my awareness, the first automated survey ("robopoll") that took a fair shot at asking the gay marriage question, notwithstanding a Rasmussen poll in 2006 that asked somewhat leadingly about the "definition of marriage". CNN's poll, by contrast, used live operators. There has been some speculation that people are apt to answer more honestly on delicate issues like gay rights when probed by a robopoll rather than a live-operator survey. Since it has become somewhat "politically incorrect" to oppose gay rights, it's possible that the automated surveys are relatively more immune from social desirability bias.

Silver doesn't think that factor entirely explains the discrepancy and notes that PPP appears to have included too few young voters, who are generally very supportive of gay marriage, in its sample. 

The most convincing point that CNN is wrong is that the only polls that matter--actual votes--in liberal states have shown majorities against gay marriage. In 2008, a little over 52 percent of California voters cast ballots to amend their state constitution in order to ban gay marriage. In 2009, 53 percent of Maine voters cast ballots to repeal gay marriage. Support for gay marriage may be increasing, but if majorities in liberal states are for banning it, that CNN poll can't possibly be right.