The National Conditions and Trial Heat model by Thomas Holbrook predicts the incumbent national two-party vote from two variables:

  1. An index of national conditions
  2. A measure of the incumbent party candidate’s performance in pre-election trial-heat polls

2016 forecast

The 2016 forecast of Holbrook’s model is that Clinton will gain 52.5% of the two-party vote, compared to 47.5% for Trump.

Vote equation

Estimated based on historical data back to 1952, the regression model’s vote equation for the 2016 election reads as:

V = 19.8 + 0.16 conditions + 0.38 trial

 Variable description

Table 1 shows the model variables and values for 2016. By adjusting the variable values in the green highlighted cells, you can see how the model forecast would change under different conditions.

Table 1: Overview of variables used in the National conditions and trial-heat model
Variable Description 2016 Value
conditions Comprised of presidential approval (Gallup) and aggregate satisfaction with personal finances (Survey of Consumers), both averaged over June, July and August of election years. Each of these components is standardized by taking their value as a percent of the highest value in the data series before averaging them.
trial Average of the incumbent party percent of the expressed two-party vote in Gallup trial-heat polls taken in the first week of September (or earliest polls in September if there were none in the first week) of the election year.  In years in which one of the nominating conventions was held in early September, the trial-heat polls are taken from the week after the last day of the convention. For 2016, the average of first-week-in-September polls listed on pollster.com is used (since Gallup has decided not to do general election trial-heat polling in 2016).
V Incumbent share of the two-party presidential vote


Holbrook, T. M. (2016). National Conditions, Trial-heat Polls, and the 2016 Election. PS: Political Science & Politics, 49(4), 677-679.