How Value-added Teacher Data Is Like a Baseball Batting Average

Neither is consistent from year-to-year, but they're among the best measures we've got for evaluating talent.

In early-September—amidst the hubbub spurred by the Los Angeles Times' release of value-added teacher assessment dataa report from the Economics Policy Institute warned that it would be "unwise" to use data pertaining to students' performance on standardized tests in making personnel decisions at a school. A new report out of the Brookings Institute says it would be unwise not to use the data at all.

The researchers behind the Brookings paper make an interesting case, drawing parallels between selective colleges' use of SAT scores in admissions, despite the fact that they don't have a strong correlation with freshman-year GPAs (about 35 percent). In the medical space, the patient mortality rates for various surgeries are published annually for hospitals and their surgeons, yet the rates aren't consistent from year-to-year more than 50 percent of the time. And, in Major League Baseball, how well a hitter bats in one year is only roughly 36 percent predictive of what he'll hit the following year.

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