The trial-heat model, developed by Jim Campbell, predicts the two-party popular vote based on the state of the economy and the candidates’ polling results.
|Table 1: Overview of variables used in the trial-heat model|
||Incumbent party’s candidate two-party support in early September Gallup preference poll||51.2|
||Annualized real GDP growth rate in the second quarter (April–June) of 2016 as indicated by the Bureau of Economic Analysis’ second estimate released at the end of August||1.1|
|V||Incumbent share of the two-party presidential vote||50.7|
The regression model’s vote equation reads as:
V = A + b1
POLL + b2
Jim Campbell presented the trial-heat model’s first forecast the at the APSA meeting in Philadelphia. The model then predicted Clinton to gain 52.1% of the two-party vote, compared to 47.9% for Trump.
In its latest update, the model predicts a virtual tie between both candidates, with vote-shares of 50.7% for Clinton and 49.3% for Trump.
Since its first application in 1992, the trial-heat model underwent only minor changes. The following chart shows the model’s forecasts and the actual election results for each election since 1992. On average across the six elections, the trial-heat model missed the final results by 2.6 percentage points.
Campbell, J. (2016). The Trial-Heat and Seats-in-Trouble Forecasts of the 2016 Presidential and Congressional Elections. PS: Political Science & Politics, 49(4), 664-668.