Monday, February 15, 2010

A potentially more reliable and up-to-date run expectancy matrix

Using Baseball Prospectus' Run Expectancy data from 2005-2009, I devised a weighted composite run expectancy for use in further analysis of marginal run expectancy changes from events.
Composite Run Expectancy By Out and Baserunners
Situation0 outs1 out2 outs
Bases Empty0.5220.2800.107
Man on 1st0.8960.5350.227
Man on 2nd1.1490.6970.333
Man on 3rd1.3950.9690.365
1st and 2nd1.5050.9220.458
1st and 3rd1.7761.1880.505
2nd and 3rd2.0201.4220.581
Bases loaded2.3011.5760.772

Assuming equal weight to each season's run expectancy totals, the above chart utilizes a somewhat arbitrary 50-30-10-6-4- scale, weighing the 2009 season most heavily (50%) down to the least-weighted 2005 season (4%) to give better credence to more recent MLB run environments.

This will be the matrix I use in any further research that requires a run expectancy matrix.

Eyeballing the variance between seasons, the data is roughly consistent across the last five years. There didn't appear to be a dramatic trend beyond a subtle, general decrease in expected runs for several events over the last five years. But I preferred to emphasize recent trends over emphasizing the distant past and recent past equally given the always-changing MLB environment.

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