Why your best sport is probably noise
Does your most profitable category mean anything?
You slice your record by sport, by book, by market, by day of week. One slice is clearly your best. It is probably nothing.
A 95% bar means a coin-flip record clears it one time in twenty per test. Run the test on several slices and the chance that at least one looks good by luck stops being small:
| Slices tested | Chance one looks real by luck | Bar it should clear |
|---|---|---|
| 1 | 5.0% | z = 1.96 |
| 5 | 22.6% | z = 2.58 |
| 10 | 40.1% | z = 2.81 |
| 20 | 64.2% | z = 3.02 |
By 14 slices it is a coin flip that something in your record looks significant when nothing is. A bettor who invents tags until one of them looks profitable is not running a test. They are running a search, and a search needs a higher bar than z = 1.96 — up to z = 3.02 at 20 slices.
What to do instead
Decide which slices matter before looking, and count every slice you tested, including the ones you abandoned. A slice under 30 settled bets should not be characterised at all — not "slightly negative", not "promising", nothing.
This is the correction essentially nobody in this category applies, and tag breakdowns are exactly where it is needed. A tool that shows you twenty segments and highlights the green ones is selling you the search results and calling them a finding.