/us-potus-model

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

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State and national presidential election forecasting model

Last update on Tuesday July 14, 2020 at 12:40 PM 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 - the final model we use for the 2020 presidential election
  • poll_model_2020_no_partisan_correction.stan - a model that removes the correction for partisan non-response bias in the polls
  • poll_model_2020_no_mode_adjustment.stan - a model that further removes the adjustments for the mode in which a survey is conducted (live phone, online, other) and its population (adult, likely voter, registered voter)

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

outlet ev_wtd_brier unwtd_brier states_correct
economist (backtest) 0.0333707 0.0302863 49 

## [1] 0.02242826

Predictions for each state

state mean low high prob se
NC 0.503 0.454 0.555 0.527 0.031
MO 0.510 0.461 0.561 0.635 0.030
IN 0.486 0.434 0.537 0.330 0.031
MT 0.483 0.427 0.534 0.297 0.031
FL 0.519 0.472 0.569 0.734 0.030
GA 0.476 0.425 0.528 0.201 0.031
VA 0.527 0.479 0.574 0.818 0.028
OH 0.527 0.478 0.576 0.818 0.029
AR 0.472 0.423 0.524 0.190 0.031
AZ 0.470 0.418 0.523 0.172 0.032
WV 0.469 0.420 0.520 0.154 0.031
NV 0.534 0.483 0.587 0.859 0.031
MS 0.465 0.412 0.522 0.134 0.034
CO 0.535 0.485 0.583 0.878 0.028
ND 0.463 0.403 0.520 0.150 0.034
LA 0.461 0.412 0.514 0.102 0.031
TX 0.458 0.407 0.508 0.092 0.030
– 0.544 0.513 0.575 0.996 0.018
SC 0.455 0.408 0.508 0.066 0.032
SD 0.453 0.401 0.506 0.074 0.031
NH 0.552 0.503 0.602 0.956 0.030
PA 0.557 0.508 0.606 0.966 0.029
WI 0.559 0.507 0.606 0.974 0.028
KY 0.440 0.391 0.491 0.030 0.031
NM 0.560 0.502 0.614 0.951 0.032
MN 0.561 0.512 0.611 0.976 0.030
TN 0.438 0.388 0.491 0.030 0.032
IA 0.564 0.512 0.612 0.978 0.029
MI 0.565 0.516 0.612 0.981 0.028
AK 0.427 0.375 0.479 0.007 0.031
OR 0.575 0.524 0.624 0.993 0.030
KS 0.424 0.375 0.475 0.009 0.030
ME 0.587 0.537 0.635 0.997 0.029
WA 0.587 0.536 0.636 0.998 0.030
NE 0.412 0.363 0.462 0.001 0.029
AL 0.407 0.359 0.460 0.009 0.031
NJ 0.594 0.543 0.644 0.999 0.030
DE 0.619 0.569 0.666 0.999 0.028
CA 0.621 0.569 0.669 1.000 0.028
OK 0.379 0.330 0.432 0.001 0.031
CT 0.623 0.576 0.670 1.000 0.028
WY 0.375 0.325 0.426 0.000 0.031
MD 0.629 0.568 0.687 0.999 0.034
IL 0.633 0.586 0.679 1.000 0.027
MA 0.636 0.586 0.686 1.000 0.030
ID 0.352 0.301 0.404 0.000 0.031
NY 0.649 0.599 0.699 1.000 0.029
UT 0.344 0.297 0.393 0.000 0.029
VT 0.660 0.611 0.707 1.000 0.028
RI 0.669 0.622 0.716 1.000 0.028
HI 0.677 0.618 0.727 1.000 0.030
DC 0.908 0.880 0.934 1.000 0.015

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

outlet ev_wtd_brier unwtd_brier states_correct
Linzer NA 0.003800 NA
Wang/Ferguson NA 0.007610 NA
Silver/538 NA 0.009110 NA
Jackman/Pollster NA 0.009710 NA
Desart/Holbrook NA 0.016050 NA
economist (backtest) 0.0327484 0.021624 50
Intrade NA 0.028120 NA
Enten/Margin of Error NA 0.050750 NA 

## [1] 0.02187645

Predictions for each state

state mean low high prob se
FL 0.497 0.450 0.542 0.468 0.027
VA 0.506 0.461 0.550 0.591 0.026
CO 0.510 0.465 0.557 0.645 0.028
OH 0.511 0.465 0.558 0.656 0.028
– 0.512 0.480 0.542 0.773 0.018
NC 0.488 0.442 0.534 0.343 0.027
NH 0.517 0.470 0.564 0.726 0.028
IA 0.518 0.473 0.561 0.749 0.026
NV 0.521 0.474 0.568 0.787 0.028
WI 0.524 0.478 0.569 0.805 0.027
PA 0.531 0.485 0.577 0.862 0.027
MO 0.463 0.416 0.510 0.095 0.028
MN 0.538 0.493 0.582 0.916 0.027
OR 0.539 0.492 0.585 0.919 0.027
AZ 0.459 0.412 0.504 0.072 0.027
MI 0.541 0.495 0.586 0.928 0.027
IN 0.458 0.413 0.504 0.062 0.027
NM 0.543 0.496 0.589 0.936 0.027
MT 0.455 0.409 0.502 0.056 0.028
GA 0.453 0.405 0.499 0.049 0.028
SC 0.441 0.386 0.496 0.043 0.033
NJ 0.559 0.510 0.606 0.975 0.028
SD 0.439 0.392 0.487 0.016 0.029
ME 0.561 0.515 0.606 0.982 0.027
WA 0.565 0.519 0.612 0.987 0.028
CT 0.571 0.523 0.619 0.993 0.029
ND 0.425 0.380 0.469 0.005 0.026
TN 0.425 0.378 0.472 0.004 0.028
NE 0.422 0.375 0.470 0.003 0.028
WV 0.418 0.368 0.469 0.002 0.031
MS 0.415 0.351 0.478 0.015 0.037
TX 0.415 0.373 0.461 0.002 0.027
CA 0.590 0.547 0.632 0.998 0.025
MA 0.590 0.541 0.637 0.996 0.028
LA 0.405 0.359 0.452 0.002 0.028
KY 0.405 0.354 0.455 0.000 0.030
KS 0.399 0.342 0.460 0.005 0.036
DE 0.604 0.549 0.659 0.997 0.033
IL 0.604 0.556 0.649 1.000 0.027
MD 0.607 0.559 0.653 1.000 0.027
AL 0.389 0.342 0.437 0.000 0.028
AR 0.378 0.333 0.425 0.000 0.028
RI 0.623 0.573 0.672 1.000 0.029
NY 0.623 0.576 0.668 1.000 0.027
AK 0.366 0.306 0.428 0.001 0.037
OK 0.339 0.290 0.393 0.000 0.032
HI 0.662 0.615 0.707 1.000 0.027
VT 0.674 0.622 0.721 1.000 0.028
ID 0.325 0.276 0.375 0.000 0.030
WY 0.317 0.250 0.391 0.000 0.044
UT 0.275 0.231 0.323 0.000 0.029
DC 0.899 0.848 0.938 1.000 0.023

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

outlet ev_wtd_brier unwtd_brier states_correct
economist (backtest) 0.084973 0.0590491 47
538 polls-plus 0.092800 0.0664000 46
538 polls-only 0.093600 0.0672000 46
princeton 0.116900 0.0744000 47
nyt upshot 0.120800 0.0801000 46
kremp/slate 0.121000 0.0766000 46
pollsavvy 0.121900 0.0794000 46
predictwise markets 0.127200 0.0767000 46
predictwise overall 0.127600 0.0783000 46
desart and holbrook 0.127900 0.0825000 44
daily kos 0.143900 0.0864000 46
huffpost 0.150500 0.0892000 46 

## [1] 0.03065481

Predictions for each state

state mean low high prob se
FL 0.501 0.458 0.545 0.512 0.026
NC 0.496 0.450 0.543 0.450 0.028
OH 0.492 0.444 0.539 0.386 0.028
IA 0.490 0.441 0.542 0.374 0.030
NV 0.514 0.467 0.560 0.667 0.028
– 0.518 0.489 0.550 0.819 0.019
PA 0.518 0.470 0.565 0.740 0.028
NH 0.520 0.471 0.567 0.745 0.028
CO 0.520 0.475 0.565 0.764 0.027
AZ 0.474 0.429 0.519 0.174 0.026
WI 0.527 0.479 0.575 0.822 0.029
MI 0.527 0.479 0.573 0.835 0.028
VA 0.528 0.483 0.573 0.847 0.027
GA 0.472 0.427 0.517 0.153 0.026
MN 0.534 0.486 0.581 0.876 0.028
NM 0.540 0.493 0.589 0.918 0.029
SC 0.456 0.411 0.501 0.054 0.027
ME 0.550 0.503 0.598 0.960 0.029
MO 0.446 0.399 0.492 0.028 0.027
OR 0.555 0.507 0.600 0.965 0.027
TX 0.442 0.399 0.486 0.019 0.026
MS 0.441 0.395 0.485 0.013 0.026
WA 0.572 0.524 0.618 0.992 0.028
CT 0.572 0.526 0.618 0.994 0.028
AK 0.425 0.378 0.471 0.006 0.027
IN 0.425 0.381 0.471 0.004 0.027
DE 0.576 0.532 0.623 0.997 0.028
NJ 0.579 0.534 0.626 0.998 0.027
LA 0.413 0.368 0.456 0.002 0.026
IL 0.588 0.543 0.632 1.000 0.026
MT 0.412 0.363 0.460 0.002 0.029
KS 0.412 0.366 0.458 0.001 0.028
TN 0.408 0.362 0.452 0.000 0.027
RI 0.593 0.544 0.639 0.999 0.027
SD 0.404 0.356 0.451 0.000 0.028
UT 0.398 0.331 0.454 0.003 0.033
NE 0.392 0.348 0.438 0.000 0.027
NY 0.609 0.564 0.654 1.000 0.027
AR 0.390 0.344 0.437 0.000 0.028
AL 0.390 0.347 0.433 0.000 0.026
ND 0.387 0.341 0.432 0.000 0.027
KY 0.379 0.334 0.425 0.000 0.027
CA 0.625 0.582 0.666 1.000 0.024
MA 0.631 0.586 0.675 1.000 0.027
MD 0.639 0.592 0.683 1.000 0.026
ID 0.359 0.312 0.404 0.000 0.027
WV 0.358 0.315 0.404 0.000 0.027
HI 0.654 0.604 0.706 1.000 0.031
OK 0.346 0.303 0.390 0.000 0.026
VT 0.674 0.629 0.719 1.000 0.027
WY 0.290 0.249 0.332 0.000 0.025
DC 0.906 0.866 0.938 1.000 0.019

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.