Forecaster's Toolbox: Team Toolbox

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Not surprisingly, the following principles all come from the annals of Bill James and his Baseball Abstracts from the 1980s.

Johnson Effect (Bryan Johnson): Teams whose actual won/loss record exceeds or falls short of their statistically projected record in one season will tend to revert to the level of their projection in the following season.

Law of Competitive Balance: The level at which a team (or player) will address its problems is inversely related to its current level of success. Losing teams/low performing players will tend to make changes to improve; winning teams/high performing players will not. This law is the explanation for the existence of the Plexiglass Principle and the Whirlpool Principle.

Plexiglass Principle: If a player or team improves markedly in one season, it will likely decline in the next. The opposite is also true but with a slightly lower frequency (because a poorer performing player will get fewer opportunities to rebound).

Whirlpool Principle: All team and player performances are forcefully drawn to the center. For teams, that center is a .500 record. For players, it represents their career average level of performance.