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A player's Percentile Forecast is a representation of the player's expected performance in the upcoming season at various levels of probability. For example, if a pitcher's 75th percentile EqERA forecast is 3.52, this indicates that he has a 75% chance to post an EqERA of 3.52 or higher, and a 25% chance to post an ERA less than 3.52. Higher percentiles indicate more favorable outcomes.
The Percentile Forecast is calibrated off of two Key Statistics: EqERA for pitchers, and EqA for batters. The Key Statistics are chosen because they provide the best representation of a player's overall value.
PECOTA runs a series of regressions within the set of comparable data in order to estimate how changes in peripheral statistics are related to changes in the Key Statistic. For example, if it first estimates that Carl Crawford will produce a .290 EqA next year, it then tries to determine what home run total, walk total, and so on are most likely to be associated with a .290 EqA season. PECOTA then iterates this result until the peripherals match ("add up to") the Key Statistic.
Important Note: The Percentile Forecasts are designed to work for the Key Statistic (EqA and EqERA) only. If a player's 90th percentile forecast for home runs is 42, this should not be read to mean that he has a 10% chance of hitting 42 home runs (or more). Rather, it means that he has a 10% chance of having a performance as valuable as the line represented by the 10th percentile forecast, whether this comes from the particular combination of peripheral statistics listed in the percentile line, or an equally valuable (but different) combination of statistics. In particular, the percentile forecasts should not be read literally for counting statistics (HR, W, etc.) because of the complicated interactions between performance and playing time.
Percentile Forecast appears in the following BP Glossary Categories:
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