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Pre-Election Polls Underestimate the Success of Women Candidates

In the run-up to 2008, there was no end of speculation about the so-called Bradley Effect or Wilder Effect — the theory that polls tend to overestimate the vote share of black candidates — and what it meant for Barack Obama. But the actual evidence for this effect is weak. Whatever effect may have existed when Tom Bradley and Douglas Wilder were running for office does not exist now.

But the 2008 and 2012 presidential elections also raise a different question: do polls accurately assess the electoral prospects of women candidates? New research by the political scientists Christopher Stout and Reuben Kline suggests they do not:

Looking at Senate and Gubernatorial candidates from 1989 to 2008 (more than 200 elections in over 40 states), we analyze the accuracy of pre-election polls for almost the complete universe of female candidates and a matched sample of white male cases. We demonstrate that pre-election polls consistently underestimate support for female candidates when compared to white male candidates. Furthermore, our results indicate that this phenomenon — which we dub the Richards Effect, after Ann Richards of Texas — is more common in states which exhibit traits associated with culturally conservative views of gender issues.

Mr. Stout and Mr. Kline find that, on average, the polls accurately estimate the vote share of white male candidates: the difference between the poll estimates and the actual election outcome are less than half a percentage point. But for female candidates, the polls underestimate their eventual vote share by over 2 percentage points, on average. For more than half of these candidates, the difference is outside of the margin of error of the polls. When the difference is greater than the margin of error, it reflects an underestimate of the female candidate’s vote share two-thirds of the time. This so-called Richards Effect cannot be explained away with other attributes, like the race of the candidates or the state of the election.

The size of the Richards Effect is larger in states with fewer women in the labor force — which suggests it stems from conservative attitudes about the place of women in politics. This leads to an interesting conclusion. Although the Bradley Effect assumes that people conceal their true opposition to the black candidate, the Richards Effect appears to work the opposite way: people conceal their true support for the female candidate, especially in areas with culturally conservative views about gender roles.

Mr. Stout and Mr. Kline note that the Richards Effect could have real consequences:

There is a well documented “bandwagon” effect in American and international politics where likely voters change their preferences from an underdog candidate to support a leading candidate in order to conform into what they perceive to be the political norm … If support for female candidates is consistently and systematically underestimated because of polling discrepancies, some voters who would have otherwise supported a woman for political office may adjust their preference to support her competitor. As a result, the Richards Effect may cause female candidates to be less competitive than they would be if polls were correctly gauging their support.

To be sure, this is speculative. Female candidates actually suffer no apparent penalty at the ballot box. As the political scientists Richard Fox and Jennifer Lawless have argued, the underrepresentation of women in higher office stems more from a gender gap in ambition and recruitment, not from sexism toward women who do decide to run for office.

But reluctance among citizens to express their support for a woman candidate — even if they might vote for her in the end — certainly does little to encourage women to run.

Correction: A previous version of this article misstated what the Bradley Effect or Wilder Effect is; it is the theory that pre-election polls tend to overestimate the vote share of black candidates – not underestimate.

John Sides is a professor of political science at Vanderbilt University and is one of the authors of “Identity Crisis: The 2016 Presidential Campaign and the Battle for the Meaning of America.”