Analyzing Obama’s Out- and Under Performance in the 2008 Presidential Elections: Social Desirability Bias, Sample Selection, and Momentum Neglect in the Polls

44 Pages Posted: 10 Jun 2010 Last revised: 21 Jul 2010

Date Written: July 20, 2010

Abstract

Using state-level poll data, we analyze Obama’s out- and underperformance of the predictions in the 2008 US presidential elections. The analyses show that the polls systematically mispredicted state margins. While they were unconditionally unbiased, i.e., accurate on average, they were conditionally biased. The stronger the frontrunner was projected to be, the more he outperformed the prediction, providing evidence for voter polarization not anticipated in the polls. We further contrast social desirability, sample selection, and momentum neglect by proposing which state-level social and demographic indicators capture which of the three biases and hypothesize the direction of the effect under the proposed biases. Numerous state-level indicators relate to Obama out- or underperforming the prediction and account for nearly 60 percent of the variance in the prediction error, falsifying that the prediction error was random. Net of other influences, Obama outperformed where unemployment and education were higher, in states with many non-English speakers, and where a greater share of people lived in nonfamily households. Obama underperformed where per-capita income was higher, where a greater share of people had no health insurance, where a greater share of people lived in metropolitan areas, and where religious diversity was low. The directions of these effects suggest that all three biases - social desirability, sample selection, and momentum neglect - may have been present in the polls. The study underscores the benefits of a theory-driven approach to jointly analyzing multiple sources of bias.

Keywords: US presidential elections, Obama, McCain, polls, biases, social desirability, sample selection, momentum neglect

Suggested Citation

Malter, Daniel, Analyzing Obama’s Out- and Under Performance in the 2008 Presidential Elections: Social Desirability Bias, Sample Selection, and Momentum Neglect in the Polls (July 20, 2010). Available at SSRN: https://ssrn.com/abstract=1623204 or http://dx.doi.org/10.2139/ssrn.1623204

Daniel Malter (Contact Author)

University of Maryland ( email )

College Park
College Park, MD 20742
United States

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