looking at elections: the bradley effect
(The latest in a series of posts aimed at explaining election stuff to all you lucky non-political scientists)
Not 20 minutes after the networks called it for Hillary Clinton in New Hampshire, I started to see mentions of the "Bradley Effect" on political blogs and news sites. The Bradley Effect refers to a phenomenon in which pre-election polls inaccurately predict an African-American or other minority candidate's percentage of the vote because voters being polled want the person asking the question to believe that they would vote for a minority candidate even though they won't.
In the case of this week's vote, this would cause us to infer that the Bradley Effect was the reason Barack Obama enjoyed a strong advantage over Hillary Clinton in the polls leading up to Tuesday's primary but still lost to Clinton. New Hampshire voters, the thesis goes, want to be seen by pollsters as progressive, open-minded people, but in reality, some of them were lying and don't actually intend to vote for the African-American candidate for whatever reason.
(A side argument on this says that perhaps that's why Obama did so well in Iowa: the social pressure and public nature of the caucuses meant that people had to take a public stand. If they want to be perceived as progressive, they had to back up what they told pollsters with their actual vote.)
I'm inclined not to buy the thesis that the Bradley Effect explains why pollsters were wrong about New Hampshire. Why? Because, as Charles Franklin eloquently explains over at Mystery Pollster, the polls were actually pretty accurate when it came to predicting how much of the total vote Obama would receive. As Franklin notes, "The standard trend estimate for Obama was 36.7%, the sensitive estimate was 39.0% and the last five poll average was 38.4%, all reasonably close to his actual 36.4%."
The mistake, therefore, was not in the predictions as to how Obama would do, but rather pollsters failed to capture how much support Hillary Clinton gained. And I don't think there's much they could have done to mitigate that; the exit poll data made it clear that a lot of voters made up their minds at the very end of the race. Among the 17% of Democratic primary voters who decided on election day, Clinton got 39% to Obama's 36%. I think those 19,000 or so votes (almost 2,000 more than Obama), added to those who decided long ago that they would vote for her, were probably enough to push her over the top. Clinton won by less than 8,000 votes.
While I have no doubt that there are many Americans who won't vote for Obama because of the color of his skin, in this case, I just don't think that's what happened. South Carolina may be more interesting in this regard, but there, I'm not sure there's an incentive for voters to lie to pollsters. Half of South Carolina's Democratic primary voters are African-American, and there's less social pressure among South Carolina whites to be seen as politically and socially progressive.