# Baseball by the Numbers: Making sense of statistics across eras

## A .300 batting average meant something entirely different in 2020 than in 2000 or 1930.

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Baseball constantly is evolving, and so are the meanings of basic stats.

A .300 batting average meant something entirely different in 2020, when the major-league average was .245, than in 2000, when it was .270, or 1930, when it was .296.

Modern metrics confront the problem of cross-era comparisons by comparing players to their contemporaries on scales that mean the same thing across eras.

One way is to measure in wins, as in wins above replacement. Another is to normalize stats to scales where 100 signifies league average, as in OPS+ or weighted runs created plus.

Using those scales, the question becomes, ‘‘How far above or below his contemporaries did a player stand?’’

Babe Ruth, with a career-record 197 wRC+, produced offense at 197% of the average for his time. No. 2 Barry Bonds produced at 173% of the average for his time.

OPS+ and wRC+ also are adjusted for ballparks, with wRC+ being more sophisticated because it gives weights to offensive events from double plays to home runs, so it correlates better to runs.

We can use either to demonstrate how values of more basic stats vary.

In 2019, White Sox shortstop Tim Anderson hit .335 with a .357 on-base percentage and a .508 slugging percentage. Add the OBP and SLG, and that’s an .865 OPS. Compared to league average and normalized so 100 is average, Anderson had an OPS+ of 128.

In 1917, Hall of Famer Eddie Collins hit .289/.389/.363. His .752 OPS was 133 points below Anderson’s, but he also had a 128 OPS+.

In 2019, teams averaged 4.83 runs per game; in 1917, the average was only 3.59. Given the context, Collins’ lesser basic numbers were as valuable as Anderson’s.

A Cubs example, using wRC+: In 1906, Frank Chance had an .849 OPS, hitting .319/.419/.430. Sammy Sosa matched that .849 OPS in 2004 with .253/.332/.517.

But in 1906, teams averaged only 3.61 runs per game, far behind the 4.81 average of 2004. An .849 OPS was a far bigger share of overall offense in 1906, and that’s reflected in Chance’s 160 wRC+ vs. Sosa’s 114.

You can do this with one player where there’s a sharp divide in context. Between 1968 and 1969, the mound was lowered and the strike zone narrowed. Runs per game soared from 3.42 to 4.07.

The Cubs’ Billy Williams had seemingly similar seasons with a .288 batting average and .836 OPS in 1968 and a .293 batting average and .828 OPS in 1969. But OPS+ and wRC+ pick up on the change. Williams’ 142 OPS+ and 143 wRC+ indicate a much more valuable 1968 than his 119 and 120 a year later.

Whether you could pluck Collins or Chance out of their times and into today’s game is a different question. Baseball has changed dramatically in who plays, where they play, travel, training, diet, sports medicine, equipment and on and on.

There’s no easy way to measure that. What we can do is measure and compare player values in their own times and put those values on scales that are meaningful across eras.

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