National Conditions, Trial-heat Polls, and the 2016 Election
Thomas M. Holbrook, University of Wisconsin,Milwaukee
The National Conditions and Trial Heat model is an adaptation of the Incumbency and National Conditions model (Holbrook 2012), which was developed to account for greater prediction error in contests in which the incumbent president was not running for reelection. The idea behind the incumbency model was that the relationship between national conditions (economic evaluations and presidential approval) should be weaker in open-seat contests than in incumbent contests; the model accounted for this with an interaction term for incumbency and national conditions. Incorporating incumbency proved to be an improvement over a straight-up national conditions model, but it only accounts for one potential explanation for discrepancies between predictions based on national conditions and actual candidate vote shares. Beyond incumbency, it is also possible that any number of election-specific, idiosyncratic factors—exceptionally good or bad candidates or campaign strategies, or unanticipated events, for instance—could lead to unexpected outcomes based on expectations from the national conditions model. The 2000 election stands out somewhat in this regard: in addition to running in an open-seat contest, the Democratic candidate, Vice-President Al Gore, seemed determined to run away from the strong economic record of the Clinton-Gore administration and not to understand that President Clinton’s still-high approval numbers could be an asset. As a result, most forecasting models—and especially those that did not use trial-heat polls—vastly overestimated Gore’s expected vote share in 2000.