Posted by Neil Paine on January 18, 2010
In a few recent posts at Basketball-Reference, I've used the method of Maximum Likelihood Estimation (MLE) to create team rankings based on W-L record and strength of schedule. I won't go into the gory mathematical details of the method here (Doug Drinen wrote a great summary at PFR a few years ago, which is better than anything I could say anyway), but the general idea is that we want to create ratings that best explain a set of past results -- we want to maximize the likelihood that if the ratings say Team A should have beaten Team B, Team A actually beat Team B in real life. These "retrodictions" are made with the following equation:
p(hW) = exp(rH - rA + HF)/(exp(rH - rA + HF) + 1)
where rH = the home team's rating, rA = the away team's rating, and HF = a home-field advantage term.
Anyway, I decided to apply this method to Major League Baseball over the past decade to rank the teams over the entirety of the 2000s. Using Retrosheet's game logs, I threw every game of the decade into a file (including regular-season and postseason games) and ran the MLE ratings; playoff games were given no extra weight, except for the fact that teams recieve bonuses in strength of schedule for the postseason, simply because they're playing the best teams. The result basically ranks the teams in an order such that, at any given point over the past 10 seasons, every team was "probably better" than the teams ranked below it. Now, let the arguments begin...
|1||New York Yankees||0.43095||1017||692||0.595||2||4||8|
|2||Boston Red Sox||0.33566||954||722||0.569||2||2||1|
|5||Chicago White Sox||0.14927||869||771||0.530||1||1||3|
|6||St. Louis Cardinals||0.14822||946||737||0.562||1||2||6|
|10||Los Angeles Dodgers||0.07101||871||772||0.530||0||0||3|
|11||San Francisco Giants||0.06250||867||775||0.528||0||1||2|
|12||Toronto Blue Jays||0.05893||805||814||0.497||0||0||0|
|16||New York Mets||-0.01021||829||813||0.505||0||1||1|
|23||San Diego Padres||-0.14105||770||858||0.473||0||0||2|
|25||Tampa Bay (Devil) Rays||-0.18623||702||931||0.430||0||1||1|
|28||Montreal Expos/Washington Nationals||-0.26496||711||908||0.439||0||0||0|
|29||Kansas City Royals||-0.27107||672||948||0.415||0||0||0|
What's probably the most striking is how clearly this shows the disparity between the AL and the NL over the past decade. If you compare the MLE ranking to the teams' winning percentages, being in the NL is worth roughly 30 points of WPct for the majority of the teams on this list; over the course of a decade, that's essentially 5 extra wins a year the average NL team got above their "true talent level" because of the weaker competition relative to the MLB average.
It's also interesting to look at the ratings by division:
|Anaheim/LA Angels||AL West||0.28842|
|Oakland Athletics||AL West||0.26743|
|Seattle Mariners||AL West||0.14430|
|Texas Rangers||AL West||0.00799|
|New York Yankees||AL East||0.43095|
|Boston Red Sox||AL East||0.33566|
|Toronto Blue Jays||AL East||0.05893|
|Baltimore Orioles||AL East||-0.18086|
|Tampa Bay (Devil) Rays||AL East||-0.18623|
|Chicago White Sox||AL Central||0.14927|
|Minnesota Twins||AL Central||0.14299|
|Cleveland Indians||AL Central||0.05296|
|Detroit Tigers||AL Central||-0.13396|
|Kansas City Royals||AL Central||-0.27107|
|Atlanta Braves||NL East||0.13685|
|Philadelphia Phillies||NL East||0.05870|
|New York Mets||NL East||-0.01021|
|Florida Marlins||NL East||-0.03519|
|Montreal Expos/Washington Nationals||NL East||-0.26496|
|Los Angeles Dodgers||NL West||0.07101|
|San Francisco Giants||NL West||0.06250|
|Arizona Diamondbacks||NL West||-0.05593|
|Colorado Rockies||NL West||-0.14006|
|San Diego Padres||NL West||-0.14105|
|St. Louis Cardinals||NL Central||0.14822|
|Houston Astros||NL Central||-0.02893|
|Chicago Cubs||NL Central||-0.08620|
|Cincinnati Reds||NL Central||-0.21235|
|Milwaukee Brewers||NL Central||-0.23670|
|Pittsburgh Pirates||NL Central||-0.37248|
Most people consider the AL West a weak division whose winner usually takes the crown by default, but the MLE ratings say it was actually the strongest over the past decade, even more so than the AL East, which was dragged down by the struggles of Baltimore and Tampa for most of the 2000s. Meanwhile, the only team in the West to finish with a sub-.500 record for the Aughts was Texas, and at .479, even their mark translates to above the MLB average when accounting for the AL's superiority. In other words, the idea that the Angels have been mopping up in a weak division by default is simply a myth.
In sharp contrast to the AL West was the entire National League, whose strongest division (the East) was actually worse than the AL's weakest (the Central). At the very bottom of the heap was the NL Central, where St. Louis racked up 6 division titles in part by being the only above-average team in a group that "boasted" 3 of the 5 worst teams of the decade by MLE in Cincinnati, Milwaukee, and Pittsburgh (the latter of which ranked dead last in MLB by a mile). It's strange to think that those teams were competitive in the 80s/early 90s, but now they consider a successful season to be the occasional brief, C.C. Sabathia-fueled playoff run or an odd 2nd- or 3rd-place finish here and there.
Shifting our attention back to the other end of the spectrum, the battle for #1 overall wasn't especially close going into 2009, and the Yankees blew it wide open by winning their 2nd title of the decade. They finished the 2000s as the only team with more than 1,000 combined regular-season and playoff wins, an MLB-best 8 division titles, and an MLB-best 4 pennants as well. Many would argue that I forgot to include an additional column for their record-shattering payroll, their advantage in which mirrors their lead in the ratings... But whatever the reason for their success, you have to acknowledge that -- by the numbers, at least -- the Yankees were the decade's most accomplished team (and this is coming from a very committed Red Sox fan).
That said, let me know what you think -- who were your top teams of the 2000s? Why is the AL so much stronger than the NL? And which teams will rise to prominence over the next decade? Give me your opinions in the comments below...