Sunday, January 28, 2007

86 wins = Division Champ?

Jeff Sackmann recently produced a good writeup of the Cubs' 2007 outlook, forecasting 86 wins for this year's Northsiders. I liked the piece except for the ending, where Sackmann decides two things: that he has been too optimistic in granting them 86 wins, and that the Cubs aren't headed to the postseason this year.

There are two basic approaches one can utilize when forecasting a team's performance: project the team's runs scored and allowed and generate a Pythagorean estimated record, or start with last year's results and adjust for the various player additions, subtractions, improvements, and declines. Sackmann used the latter approach, and though he simplified the process by using round numbers, his methodology is solid and it produces an accurate result.

Two other blogs went the former route, and got virtually the same estimates: Baseball Musings and Viva El Birdos. My personal numbers portend 86-87 wins, depending on some playing-time adjustments, so I think we're in agreement about the team's talent level.

Now that that's settled, what of the Cubs' chances to make the playoffs or win the World Series with 86-win talent? A title certainly isn't out of the question--the last two Fall Classic winners were forecast for 86 wins or fewer by PECOTA. Many, however, are arguing that 86 wins won't be enough to top a division, especially one with six teams. They're probably right; it's very likely some team in the NL Central will end up with more than 86 wins this time around.

That doesn't mean the Cubs won't make the playoffs.

Although playoff teams average something like 95 regular-season wins, this doesn't mean they are, on average, teams with 95-win talent. This is because the teams that finish with the best records usually get there through a combination of talent and good fortune. Just as the 2001 Mariners would not win 116 games if they had to play that season's schedule over again, the typical playoff team would be expected to win fewer than 95 games if they had a do-over. Like the infinite number of monkeys with typewriters, baseball teams occasionally produce a playoff season out of sheer randomness. The good teams have a head start, but the beauty is that, recent AL and NL East divisions aside, the underdogs still have their chances.

Back to the Cubs. 86 wins is simply a mean forecast; there's roughly a 50% chance they'll win more games than this, and perhaps a 25% chance they'll win 92 or more. Though the division winner may end up with 92 victories, no NL Central team has a mean projection this high, nor are they close. In fact, I don't have a single NL team rated at 89 wins or more. Someone in the NL will win more than 89 games, of course; even if every contest was a pure coin flip, simple variance would usually create at least one 90-win team, along with some 70-win teams.

In fact, even with perfect knowledge of a team's talent, the standard deviation of its win forecast is more than six games over the course of a season. (This figure is approximately .5*rt(162), or 4.5*rt(2).) This means that if we know the Cubs are an 86 win team, no more, no less, they will still finish with more than 92 wins about 16% of the time and fewer than 80 another 16%. Here's an excellent BP piece on randomness in team standings.

In reality, the best projections have a standard deviation of eight games per season, so we can adjust those parameters to 16% over 94 and 16% under 78. If you think this sounds too inaccurate, consider that the Cubs were almost universally projected for 83-87 wins last year, and we all know how that turned out.

I project the Cubs at 86 wins, the Cardinals and Brewers (yes, the Brewers) each at 84, with the rest of the division well behind. Obviously, those will not be the exact final standings. We're more likely to see the top three teams in the division produce something like 96, 89, and 84 wins respectively. But who will those teams be? We don't know yet; that's why they play the games. The numbers suggest the Cubs are, by a hair, the most likely team to take that top spot. 86 wins isn't enough to make the playoffs, but it's enough to give them a head start on the competition.

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