On the Overreport Bias of the National Election Study Turnout Rate

Consumers of the National Election Study (NES) should be concerned if the survey has a bias that is increasing with time. A recent article by Barry Burden claims that for presidential elections, there is an increasing overreport bias, or turnout gap, between the NES turnout rate and the observed turnout rate caused by declining NES response rates. I show that the increasing turnout gap is an artifact of the universes these two turnout rates are based on. Reconciling the two universes shows no systematic increase of the reconciled turnout gap in presidential elections from 1948 to 2000, and furthermore demonstrates that the post-1976 rise in NES response rates (until 2000) is rewarded in a lower turnout gap. In addition, I offer another theory to explain the turnout gap. If respondents have an equal propensity to misreport that they voted when they did not, as turnout declines, the number of nonvoter respondents increases and so does the turnout gap. I show that in multivariate analysis this theory outperforms Burden's response rate driven theory, though neither theory reaches statistical significance.