The final AggPro results are listed in the table below. They are significantly better than I expected. In each year AggPro is more accurate than any of the constituent systems. Furthermore, each year it more accurate than a theoretical projection system that would be composed of the best constituent projection for each statistical category. Finally, AggPro's projection in every category for every year is more accurate than the any constituent system's projection for a given category in a given year except for one category in one year. (
As of June 29th PECOTA's projections for this year (2009) for triples are less than 1% more accurate than AggPro's 2009 projections for triples.) These observations seem to show that these different constituent projection systems work in a complementary nature (i.e. the overall aggregate projection is more than just the sum of its best parts.)
Recall, the AggPro projections were formed by determining the weights for the constituent systems that minimized the standard error from the actual Major League Baseball data for 2007 and 2008. We were able to evaluate the AggPro projections for 2006 because AggPro does not weight the CHONE projections at all. The CHONE projections were the only constituent projections missing for 2006.
| Year | AggPro Improvement over BCPS | AggPro Improvement over TPS |
| 2006 | 5.25% | 5.00% |
| 2007 | 4.25% | 2.65% |
| 2008 | 5.90% | 4.60% |
| 2009 (through 06/29/09) | 2.4% | 2.0% |
Table Legend: BCPS = Best Constituent Projection System; TPS = Theoretical Projection System
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