3 ms·
Probably not quite 24 heads (or tails), but close! I had to dig into this for work, and doing statistics on runs is surprisingly interesting. Suppose you've go
by mattkrause 7y ago
Probably not quite 24 heads (or tails), but close!
I had to dig into this for work, and doing statistics on runs is surprisingly interesting. Suppose you've got a sequence of $n$ events, each of which 'succeeds' with probability $p$. The expected length of the longest run is approximately $\log_{1/p}(n*(1-p) + 0.577 \ln(1/p) - 1/2$. For a fair coin with $p$ = 0.5, this reduces to log_2(n) - 2/3, which is about 19 for one million events. Amazingly, the variance only weakly depends on n, but is about 2 for p=0.5.
Thus, you're probably not going to see a 24 head run in 1M events. I'm excited I got to use this information, as the project I learned it for was a total bust.
More here: Shilling (1990, College Math. J.) https://www.csun.edu/~hcmth031/tlroh.pdf https://www.csun.edu/~hcmth031/tlroh.pdf
- LeifCarrotson 7y agoIt's just 2^24 for probability 1/2, right?
- aplummer 7y agoIt’s a different calculation Matt is doing. You are calculating the probability of that run happening now. Matt is calculating the expected length of the longest run in 1 million tosses.
- mattkrause 7y agoExactly! (Thanks!) The distinction is important because a sequence of ten heads seems 'rare' in isolation. However, it is not particularly unusual when you go looking for it as a subsequence of some bigger set of trials.