Will Wednesday's release of Obama's long-form birth certificate put an end to the birther myth?
The odds aren't good. The problem is that people can be extremely resistant to unwelcome factual information...
Given how much evidence is already available, it's hard to see why a long-form birth certificate would suddenly change the minds of people who are predisposed to believe in the myth. The hardcore are already shifting to new rationales for questioning Obama's right to hold office and deconstructing the PDF released by the White House for supposed evidence of forgery.
As expected, the fringe continues to search for rationales to discredit the birth certificate -- the birther movement isn't going away. However, the Washington Post released a poll conducted after the birth certificate's release (but before news of Osama bin Laden's killing was released) showing that that birther beliefs dropped by half compared to April 2010:
I've been waiting to see if any other polls were conducted, but it looks like the Post is the only media outlet that polled on this issue. Since bin Laden's killing created a bounce that will affect responses to questions about Obama for a while, it's probably the only clean pre-/post-comparison of birther beliefs that we're going to get.
So why was this correction so effective when others tend to fail? (PDF) The answers aren't entirely clear yet, but here are some initial thoughts. First, the birth certificate's release was an unusually definitive debunking that became a major news event, so there was saturation coverage of some very strong corrective information. Second, no prominent elites on the right contested the validity of the birth certificate, which meant that coverage of its release was almost entirely one-sided. Finally, it's possible that support for the myth was soft because poll respondents didn't really believe it but were using poll questions about Obama's religion and place of birth as a way to express disapproval (as some commentators and pollsters have argued).
Does this mean that people's minds can be changed? Yes (though I will be curious to see if these effects hold over time). In cases where the first and second conditions described above hold (very strong corrective information, saturation coverage, no elite controversy), it is possible to convince people who aren't hardcore believers and conspiracy theorists. However, these conditions rarely materialize for prominent political misperceptions, which tend to be controversial among elites and harder to definitively debunk.
To underscore why misperceptions are so difficult to correct, consider the case of the Duelfer Report, a comprehensive CIA-commissioned report released in September 2004 which found no evidence that Iraq had weapons of mass destruction or an active weapons of mass destruction program. Even though the release of the report was a major news story confirming that Iraq did not have WMD, no one could not prove they hadn't been hidden, moved to Syria, etc. and conservatives continued to dispute the claim. As a result, half of Americans were still telling pollsters that Iraq had WMDs as late as 2006.
In short, the release of the birth certificate is something of a best-case scenario for misperceptions. The Post poll results are a victory to be celebrated, but we should be cautious about extrapolating from this case to other, more stubborn myths.
Update 5/13 2:03 PM: Gallup just released a poll conducted May 5-8 (after bin Laden's killing) confirming that birther beliefs were cut roughly in half:
As in the Post's poll, Gallup found that the decline was most significant among Republicans (who were most likely to endorse the claim before the release of the birth certificate):
These results are an encouraging sign that the effects of the birth certificate's release are persisting, though we should be cautious given that the Gallup poll was conducted after bin Laden's death.