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Showing posts from June, 2019

### Beat the Streak: Day Seven

In this blog post, I discuss questions of the form: “Does batter X perform better at home or away?   At day or night?   Against lefties or righties? On Friday or Monday?”   What I found was a little bit surprising.   Take for example the batter Daniel Murphy.   When you look at his data from 2011 - 2017, you will see that he got a hit in 29.85% of 1424 plate appearances during day games and he got a hit in 26.97% of 2673 plate appearances during night games.   This is a pretty meaningful difference, but is it statistically significant?   In other words, could this difference be explained purely by chance?   To answer this question, we can perform a chi squared test under the null hypothesis that the true probabilities are the same.   When we do this we get a chi squared value of 3.35 and a corresponding p value of 0.067.   Thus, we can reject the null hypothesis that the true underlying probabilities are the same at the 90% confidence level.   This is pretty convincing evidence th