Score your own predictions
You said 60% home win and it finished level. Were you right, wrong, or somewhere in between? Picking a winner can't tell you. The chance you gave to what happened can.
Your forecast
Draw, the rest:
Try an example
How to read it
- Set your chances for a home win and an away win; the draw is whatever is left.
- Pick what happened. The bars show the chance each forecaster gave it. The more you gave it, the better your forecast did.
- Knows nothing gives every result a third. League averages gives every match the usual Scottish top-flight split: 43.7% home, 23.7% draw, 32.6% away (the baseline on the SPFL Prediction Board). Beat both and your view of the match added something.
- Never give a result 0%. If it happens, your forecast is as wrong as a forecast can be.
How the three scores work
Write your forecast as \(p_H, p_D, p_A\) and what happened as \(o_H, o_D, o_A\), with 1 for the actual result and 0 for the others.
$$\text{log loss} = -\ln(p_{\text{actual}})$$ $$\text{Brier} = \sum_{k} (p_k - o_k)^2$$ $$\begin{aligned} \text{RPS} = \tfrac{1}{2}\big[&(p_H - o_H)^2 \\ &+ (p_H + p_D - o_H - o_D)^2\big] \end{aligned}$$In plain football
- Log loss only looks at the chance you gave to what happened, and punishes a low one hard. Say 0% and be wrong, and it is infinite.
- Brier checks all three of your numbers against what happened and adds up the squared misses.
- RPS knows a draw sits between a home and an away win, so backing the draw when the away side wins costs less than backing the home side.
One match proves very little
A 60% favourite that loses hasn't shown the forecast was bad: it should lose four times in ten. Forecasters are judged on their average score over hundreds of matches. The research on evaluating prediction models does exactly that for eleven predictors over 5,258 matches. To try it on real matches against the bookmaker, play Can you beat the bookies?
Why never say 0%
Try "Never say never". Ninety per cent on the home side is a strong but reasonable view. Zero per cent on the away side is a claim that it cannot happen, and when it does, log loss has no finite answer. Even the most one-sided match deserves a few per cent for the upset.