> The std. dev. of a binomial is sqrt(n p (1-p)). So for 19 coin flips that's ~2.2, or 11%, not 23%. You are correct. The usual way in which std dev is applie

> The std. dev. of a binomial is sqrt(n p (1-p)). So for 19 coin flips that's ~2.2, or 11%, not 23%. You are correct. The usual way in which std dev is applied is ± sigma accounts for about 68% of the trials, which is 2 std deviations, and is what I had in mind. So for 19 people flipping a coin, you'll have a range of about 23% variation. That factor of 2 does not change the message.