### 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