A dynamic multilevel Bayesian model to predict US presidential elections

State and national presidential election forecasting model

Last update on Thursday June 11, 2020 at 07:37 AM EDT

Code for a dynamic multilevel Bayesian model to predict US presidential elections. Written in R and Stan.

Improving on Pierre Kremp’s implementation of Drew Linzer’s dynamic linear model for election forecasting (Linzer 2013) , we (1) add corrections for partisan non-response, survey mode and survey population; (2) use informative state-level priors that update throughout the election year; and (3) specify empirical state-level correlations from political and demographic variables.

You can see the model’s predictions for 2020 here and read how it works here .

File dictionary

In terms of useful files, you should pay attention to the 3 scripts for the 2008, 2012 and 2016 US presidential elections are located in the scripts/model directory. There are three R scripts that import data, run models and parse results:

final_model_2008.R
final_model_2012.R
final_model_2016.R

And there are 3 different Stan scripts that will run different versions of our polling aggregate and election forecasting model:

poll_model_2020.stan
poll_model_2020_no_partisan_correction.stan
poll_model_2020_no_mode_adjustment.stan

The model diagnostics displayed below are all results of the poll_model_2020.stan script.

Model performance

Here is a graphical summary of the model’s performance in 2008, 2012 and 2016.

2008

Map

Final electoral-college histogram

National and state polling averages and the electoral college “now-cast” over time

States’ partisan leans over time

Model results vs polls vs the prior

Performance

## [1] 0.02242826

Predictions for each state

2012

Map

Final electoral-college histogram

National and state polling averages and the electoral college “now-cast” over time

States’ partisan leans over time

Model results vs polls vs the prior

Performance

## [1] 0.02187645

Predictions for each state

2016

Map

Final electoral-college histogram

National and state polling averages and the electoral college “now-cast” over time

States’ partisan leans over time

Model results vs polls vs the prior

Performance

## [1] 0.03073332

Predictions for each state

Cumulative charts

Calibration plot

Licence

This software is published by The Economist under the MIT licence . The data generated by The Economist are available under the Creative Commons Attribution 4.0 International License .

The licences include only the data and the software authored by The Economist , and do not cover any Economist content or third-party data or content made available using the software. More information about licensing, syndication and the copyright of Economist content can be found here .