MLB: how good are 100-win teams?

Here's a study (.pdf), called "On Why Teams Don't Repeat," that I wrote 18 years ago, before I was born. It originally appeared in the February, 1989 issue of "Baseball Analyst," the journal of sabermetrics edited by Bill James.

The idea is this: teams that make the playoffs often fail to repeat the next year. Why? Because they probably were mostly lucky the first time.

Suppose a team won 100 games. How good a team was it in terms of talent? The answer: probably less than a 100-game talent. Either it was a less-than-100 talent that got lucky, or it was a more-than-100 talent that got unlucky. But since there are many more below-100 teams than above-100 teams, it was probably on the lucky side.

The question is, *how much* less than 100 games? To find out, I tried to find a distribution of talent that would roughly approximate the actual distribution of AL wins from 1961-1984. Once I found that, I figured the chance of the 100-win team coming from each segment of that distribution. Then I figured the average.

The results:

The average 100-win team is really only a 93-win team.

Other interesting results:

The average 81-81 team is really an 82-80 team.
The average 62-100 team is really a 66-96 team.
The average 116-46 team is really a 102-60 team.

There is a 79% chance a 100-62 team was lucky.
There is a 32% chance a 65-97 team was lucky.

All these figures are approximate, of course. And circumstances have changed since 1984; now, financial imbalance means there are probably more extreme teams (at both ends of the talent scale) than there were previously, which means the amounts of luck found here might be overestimates in today's MLB.

Also, of course, there is an easier way to estimate the SD of talent, as seen here.