18 wins out of 30 is "a 60% win rate", but the 95% interval runs from 42% to 76%. Enter your rounds and wins to see the interval; then enter the win rate you hope to prove to see how many rounds it takes.
| Observed win rate | — |
| 95% confidence interval | — |
| Interval width | — |
While the interval contains 50%, this sample cannot tell you from a coin flip.
| Rounds needed, roughly | — |
Two-sided 5% significance, 80% power, against 50%. The closer to 50%, the faster the requirement grows.
Method and derivation in How many trials are enough; build the sample with free practice.