## Friday, August 03, 2007

### 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.

At Friday, August 03, 2007 5:40:00 PM,  Brian Burke said...

Coincidentally, I'm in the middle of posting some very similar stuff on luck in NFL game outcomes. Of course, you're 18 years ahead of me!

I found that in about 50% of all games, luck was the deciding factor rather than the relative strength of each team.

I compared a pure binomial distribution, a simulated pure-skill (zero luck) distribution, and the actual distribution of NFL records since the '02 expansion.

I synthesized the pure-luck and pure-skill distributions together in varying degrees. (10% luck & 90% skill, 20% luck & 80% skill, etc.) until I maximized the goodness of fit between the actual distribution and my synthesized distribution.

At 52.5% luck, the distribution is nearly indistinguishable from the real distribution (chi-square goodness of fit p=0.94)

I admit 52.5% seems very high. But keep in mind, sometimes the better team wins only by luck.

My stuff is here, but I've only posted 2/3 of the study so far: www.bbnflstats.com

At Thursday, September 01, 2011 12:36:00 AM,  Anonymous said...

This without question one of the dumbest comments on sports statistics I've ever seen. "The average 100-win team is really a 93-win team." The average 100-win team is a 100-win team.

Of course luck plays a factor, but physical skill, teamwork, managerial decision making, and so on, are far more important than luck in determining the outcome of each play, which collectively determines the outcome of each game, which in turn directly determines the final record of the team.

Luck is the randomness or chance in the game. In poker, for example, there is much more randomness, than in, say, a game of chess. Over time, pitchers with consistent winning records, hitters with consisistent batting averages, and fielders with consistent fielding stats indicate the amount of luck or the amount of skill in baseball. I suspect that the luck factor is not high enough to indicate that 100-win teams are not really 100 win teams.

If exactly the same teams played the season over again, what are the chances that a 100-win team would have 100 wins in the second go round? What if they played the exact same season over again 100 times, such as is done in computer simulations? How may of the 100 times would result in 100-win seasons?

It is the calibre of play of each athlete and of the team as a whole relative to the same for opponents, and not luck, that determines whether or not a team wins 100 games in a 162 game season.

To quote Casey Stengel, "1/3 you win, 1/3 you lose, and it's the third in the middle that makes the difference." The outcome of that third in the middle is primarily determined by a team's relative quality of play, which is the difference between a team that wins 54 games and a team that wins 108 games.

A 100-win MLB team is a damn good baseball team -- good because of a lot of talent and hard work, not good because they were lucky.