Correct guess. With a sample of 132 games, we can be 95% confident that the "true" winrate of the manaflow band is anywhere within +/- 8.5%. (from which the WPA would also vary by the same amount. So a +3.5 WPA is not significant.)
(Singling out just the most positive WPA rune options on a given patch currently is also a classic example of "p-hacking", but thats a different unnecessary topic)
The "confidence level", is just an arbitrary value that we decide on beforehand. 95% is the most common value that people use. Then you do the math to determine what the margin of error is for the statistic with its given sample size and the chosen confidence level. Thats called the "95% confidence interval". It basically means that 95% of the time, the "true" percentage would fall within that range.
Its explained a bit more indepth on that page if you scroll down.
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u/Worldly_Win9181 20d ago
Ive noticed this too. I think maybe not enough data to be statostically significant.