Hit Rate and Small Samples: The Wilson Range Explained
What a hit rate counts
If a player has gone over 24.5 points in 7 of his last 10 games, his hit rate at that line is 70%. It counts what already happened at that exact number, in games he played. It does not say what will happen in the next game, and it is history, not a pick.
Why ten games is a wide range
Ten games is a small sample. If the player's true rate were 70%, a run of ten games could easily show 5 hits or 9. The Wilson score interval turns a count into a range that reflects how few games you have. Probetrics prints a 90% Wilson range beside the rate.
After 10 games the range is 44% to 87%: it takes in an even 50/50 and a near-certain hit. After 100 games the same rate sits in 62% to 77%. Even a perfect 5 for 5 has a 90% range of 65% to 100%.
Read it against the books' price, not 50%
A hit rate means little without a yardstick. Comparing it with 50% ignores that the line and price already reflect how good the player is. Probetrics compares a player's hit rate with the books' no-vig chance of the over at the same number, and colors the rate only when the gap is meaningful and there are enough games. A rate a few points above the fair chance over ten games is well inside the noise.
Questions and answers
- What is a good sample size for a hit rate?
- There is no cutoff, only a range that narrows as games are added. Under about ten games the 90% range is very wide; the site marks thin samples and dims them for that reason.
- What is a Wilson interval?
- A method for the range a true rate could plausibly sit in, given hits out of games. Unlike the simple plus-or-minus formula it stays sensible near 0% and 100% and with few games.
- Does a high hit rate mean the over will hit?
- No. It describes past games at that number. Lines move to reflect a player's role and form, and a small sample can look extreme by chance.
Read next
- Player prop lineA player prop line is the number a sportsbook posts for one player's stat in one game, such as 24.5 points, with a price on the over and a price on the under.
- No-vig oddsNo-vig odds, also called fair odds, are a two-sided price with the sportsbook's margin (the vig, or juice) taken out, so the two sides' chances add up to 100%.
- CalibrationCalibration is whether stated probabilities match what happens: of the picks a model gave about 70%, about 70% should win.
- Line movementLine movement is the change in a prop's posted number or price between when a sportsbook first posts it and now, and on Probetrics "moved" compares today's consensus number with the first one we stored.
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