Historical Era Adjustments
Intermediate
10 min read
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Nov 28, 2025
Historical Era Adjustments
Comparing players across eras requires adjusting for vastly different run environments, ballparks, and competition levels.
Key Adjustment Factors
- League Run Environment: Runs per game varies significantly
- Park Factors: Some parks inflate stats dramatically
- Competition: Talent pool and integration factors
- Equipment/Rules: Dead ball, juiced ball eras
Run Environment by Era
| Era | R/G | Adjustment |
|---|---|---|
| Dead Ball (1900-1919) | 3.8 | +25% |
| Live Ball (1920-1941) | 5.0 | -5% |
| Integration (1947-1960) | 4.4 | +8% |
| Expansion (1961-1976) | 4.0 | +15% |
| Steroid Era (1994-2008) | 5.1 | -8% |
| Modern (2009+) | 4.4 | Baseline |
Key Takeaways
- Always use era-adjusted stats for comparisons
- Park factors can swing stats 15-20%
- OPS+ and ERA+ are already era-adjusted
- WAR includes era context implicitly
Discussion
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