Using the data we've got, there are several ways we can evaluate the performance of a forecast:

- How closely did it predict the overall result?
- How many seats did it predict correctly?
- How accurately did it predict vote shares across all parties across all seats?

Why does this matter? Forecasting sets narratives; and people made decisions based on these forecasts.

Find all the code for this analysis in build_leaderboard.py.

How closely did each forecast predict the overall distribution of seats?

The score is the root mean squared error of the number of seats predicted for each party.

Model | Score |
---|---|

Britain Predicts (New Statesman) | 7.4 |

Manifold | 8.9 |

Exit Poll | 9.9 |

YouGov | 10.2 |

More in Common | 10.4 |

electionmaps | 11.1 |

The Economist | 11.2 |

JLP | 13.0 |

Sam Freedman | 14.8 |

Focaldata | 14.9 |

The FT | 16.2 |

Ipsos | 19.4 |

Electoral Calculus MRP | 26.4 |

WeThink | 26.9 |

Electoral Calculus STM | 29.6 |

Survation | 34.6 |

Savanta | 45.0 |

How many seats did each forecast predict correctly?

The score is the percentage of seats that were called correctly.

Model | Score |
---|---|

YouGov | 573 (90.8%) |

electionmaps | 569 (90.2%) |

Sam Freedman | 564 (89.4%) |

The Economist | 555 (88.0%) |

Manifold | 555 (88.0%) |

Exit Poll | 552 (87.5%) |

Britain Predicts (New Statesman) | 551 (87.3%) |

Focaldata | 551 (87.3%) |

More in Common | 548 (86.8%) |

JLP | 540 (85.6%) |

Electoral Calculus STM | 538 (85.3%) |

The FT | 538 (85.3%) |

Ipsos | 538 (85.3%) |

Survation | 531 (84.2%) |

Electoral Calculus MRP | 508 (80.5%) |

Savanta | 497 (78.8%) |

WeThink | 497 (78.8%) |

How accurately did each forecast predict vote shares across all parties across all seats?

The score is root mean squared error of the vote shares across all parties across all seats.

Model | Score |
---|---|

YouGov | 3.2 |

The Economist | 4.0 |

electionmaps | 4.1 |

Focaldata | 4.5 |

JLP | 4.5 |

Electoral Calculus STM | 4.5 |

More in Common | 4.5 |

Survation | 4.8 |

The FT | 4.9 |

Britain Predicts (New Statesman) | 5.0 |

Ipsos | 5.1 |

Electoral Calculus MRP | 5.3 |

WeThink | 5.3 |

Savanta | 5.8 |