There’s been a lot of talk lately about how the Yankees, under Brian Cashman, have gotten younger since 2005. For example:
Average age of Yankee pitchers
Average age of Yankee hitters
Of course, the only issue here is sample size. For example, in 2005 the Yankees had Randy Johnson (age 41), Kevin Brown (age 40), Al Leiter (age 39), Buddy Groom (age 39), Mike Stanton (age 38) and Mike Mussina (age 36) on their pitching staff for most of the year. Given the small size of a pitching staff, having these 6 very old pitchers on the team would naturally bump up the average age of the staff.
Think of it this way – say you had 18 numbers…12 of them being the number 3 and the other 6 being the number 12. Now, the average of all those 18 numbers would be 6. But, in reality, the majority of those numbers (12 of 18) were the number 3. So, seeing the average number (6) tells you little about the majority of the group.
Or, in other words, a few old apples can easily ruin the average age of the whole barrel.
Basically, it’s the difference between using the mean and median to look at a data set. And, I would suggest, in a study like this, it makes more sense to use the median rather than the mean.