Shrinking Standard Deviation
March 12th, 2009 by
Earlier I hypothesised an answer to Joe Posnanski’s question as to why many more people who played in 1930 made the Hall of Fame versus the people who played in 1980. I suggested it had something to do with a shrinking standard deviation. Here’s the data to back up my claim. I looked at all players with 400 AB in a season over a ten year span. From 1926 to 1935, there were 966 player seasons that qualified. From 1976 to 1985, there were 1472 such seasons. The results:
| Stat | 1930 | 1980 |
|---|---|---|
| Data Mean | .300 | .274 |
| Standard Deviation | .033 | .027 |
| BA, 1 SD Above Mean | .333 | .301 |
Since .300 was and is our gold standard for batting average, it was a lot easier to look good in the era centered on 1930 than 1980. Basically, the voters didn’t adjust for the higher offensive era very well.
Source:Shrinking Standard Deviation
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