Grove Insight
Graded against the actual result across 45 races (from 58 polls, through 2012).
Head-to-head vs VotePredictor Elections
The fair, apples-to-apples test: on the 44 races Grove Insight actually polled, how its final poll's margin compared to what VotePredictor Elections predicted for those same races.
| Model | Avg miss (pts) | Called right |
|---|---|---|
| Grove Insight | 5.14 | 89% |
| VotePredictor Elections | 3.40 | 80% |
VotePredictor Elections aggregates all the pollsters, so it's expected to beat any single one on margin — that's the value of averaging. The honest comparison among forecasters is on the combined board.
Every race (45)
Each race Grove Insight polled, scored on its final poll — the call right before the vote — against the actual Dem−Rep result. Click a race for its full detail.
Accuracy by time to election
Lower is better. Time to election runs right (election week) to left (~2 months out).
By the numbers
| Time to election | Polls | Avg miss | vs field | Called right |
|---|---|---|---|---|
| ≤1 wk | 4 | 1.79 | -2.45 | 100% |
| 1–3 wk | 22 | 3.29 | -1.77 | 86% |
| 3–6 wk | 20 | 5.19 | -0.51 | 90% |
| 6–9 wk | 12 | 6.38 | +0.24 | 83% |
vs field is this pollster's average miss minus all pollsters' at the same lead time — green beats the field, redtrails it. Our historical polls reach ~2 months out; earlier polling isn't in the record.
Track record by cycle — getting better?
| Year | Polls | Avg miss | Lean (house effect) |
|---|---|---|---|
| 2006 | 8 | 5.2 | D+0.5 |
| 2008 | 14 | 3.4 | R+0.4 |
| 2010 | 11 | 9.2 | D+9.2 |
| 2012 | 24 | 2.8 | D+1.0 |
Do we credit a pollster for fixing its bias? Each cycle, the model re-estimates every pollster's lean from all its earlier polls (walk-forward) and subtracts it before using the poll. We tested weighting recent cycles more — it doesn't help: a pollster's lean in one cycle barely predicts the next (correlation 0.28), so the swings above are mostly noise, and averaging over more history beats chasing the latest cycle. The all-time estimate we use came out within ~0.5% of the best option.