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Rating the MLB Divisions for 2009

Two simple ways to rate the strength of the 6 MLB Divisions are to add up the games over .500 (call this "G500") and the Run-Differentials ("RunDiff") for each Division. For the 2009 season:

          G500  RunDiff
AL-East    32     239
AL-Cent   -48    -206
AL-West    40     112

NL-East   -20     -39
NL-Cent   -34    -217
NL-West    30     111

AL-TOTAL   24     145
NL-TOTAL  -24    -145

So, based *solely* on these numbers, one would strongly expect the NL champ to come from the NL-West, and somewhat less strongly expect the AL champ to come from the AL-East.

One can use the G500 numbers to tweak teams' W-L record:  divide the Divison G500 by the number of teams in that division, divide by 2, add to the actual W-L record.  
Then the actual # wins in the AL:
    NYY=103, LAA=97, BOS=95, Min=87
become   NYY=107, LAA=102, BOS=99, Min=82

For the NL:  LAD=95, Phi=93, Col=92, STL=91
become:  LAD=98, Phi=91, Col=95, STL=88

We can also try to combine the two predictors (G500 and RunDiff) into a single "Strength" number for each Division.   The overall ratio of the absolute magnitude (i.e., ignoring the sign) of RunDiff to GB500 is about 4.5.   So if you want to weight the 2 predictors equally, multiply GB500 by 4.5.  Making the assumption that GB500 has more luck involved than RunDiff, we choose to multiply GB500 by only 2.  Then:
             Strength = 2*GB500 + RunDiff

          Strength
AL-East     303
AL-Cent    -302
AL-West     192

NL-East     -79
NL-Cent    -285
NL-West     171

AL-TOTAL    193
NL-TOTAL   -193
-------------------------------------- 

Yet another predictor is to use the 'expected' W-L records based on Runs scored and Runs allowed;  there are various flavors of this 'Pythagorian' predictor, we use the one from mlb.com.  Then the Games-above-.500 become:

          G500 
AL-East    44 
AL-Cent   -40 
AL-West    18 

NL-East     4 
NL-Cent   -42 
NL-West    24 

AL-TOTAL   22 
NL-TOTAL  -14 
 

We can use these new G500 numbers to once again tweak teams' *expected* W-L record:  divide the Divison G500 by the number of teams in that division, divide by 2, add to the *expected* W-L record.  
Expected # wins in the AL:
    NYY=95, LAA=92, BOS=93, Min=86
become   NYY=99, LAA=94, BOS=97, Min=82

For the NL:  LAD=99, Phi=92, Col=90, STL=91
become:  LAD=101, Phi=92, Col=92, STL=87

Finally, a rough correction for AL vs. NL:
AL - NL = 36; divide by 2 ==> 18
# interleague games ~ 18*14 = 252
Normalizing to a 162-game season ==> 18 * (162/252) = 12 Wins
Then the AL estimate becomes   NYY=111, LAA=106, BOS=109, Min=94

Approximate odds of Yanks winning the 2009 World Series

The following ignores several effects, just a simple estimate!

Yanks win % over Minn = 0.600 in one game (based on regular season).
In THREE-game series, add up P for the winning 4 of the 8 sequences, get 0.650
In 5-game series, add up P for the winning 16 of the 32 sequences, get 0.683
(binomial distribution ==> P=0.710   for 7-game series)
Add a bit for 5th game at home ==> 0.700
Strength of 3 starters ==> maybe 0.750.
AL-East is stronger, ==> make it 0.800

In 2nd and 3rd (7-game) series, crudely estimate 0.60 and 0.70

0.80 * 0.60 * 0.70 = 0.34 (34% chance of winning WS).