Today we talked about one big idea and then had our 2nd Fathom lab.
THE BIG IDEA:
When you hear that some historical player had a .372 batting average, you should ask ...
1. When season did the player get this batting average?
2. Where did the player play ? (The ballpark could have influenced his batting average.)
3. How many at-bats? (We'll see that it is easier to get a high batting average with a small number of at-bats.)
To really understand the greatness of a historical batting average, we look at the player's average in the context of all batting averages of regular players that season. If we compute the mean and the standard deviation of the batting averages, then we compute the z score
z = (AVG - mean)/s
This tells you how many standard deviations the guy's AVG is above or below the mean. If z = 4, that is a wow -- his batting average is four standard deviations above the mean.
In the Fathom lab, we compared the offensive stats of the American League teams and the National League teams this season. We learned that the AL teams tend to score more runs per game. The slugging percentages of the AL teams are pretty similar to the slugging pcts of the NL teams, but the AL teams seem to be better in getting on base. Since the AL teams tend to be better on OBP, they tend to score more runs.
Why is the AL better? There are likely several explanations, but the fact that the AL has the DH probably helps them score more runs.