The dispute over methodology explains the importance of this summer’s research on Seattle’s minimum-wage experiment. The city’s wage floor, previously about $9.50 an hour, has been raised to $13 and is on its way to $15. A comprehensive study by academics at the University of Washington estimated that the higher minimum “reduced hours worked in low-wage jobs by around 9 percent.” Consequently, earnings for these employees actually dropped “by an average of $125 per month.” What’s especially inconvenient for minimum-wage proponents is that the Seattle study used a “close comparison” method similar to the one they have favored for years. The authors of the study compared workers in Seattle with those in other metropolitan areas in Washington, like Olympia, Tacoma and Spokane. To no one’s surprise, that hasn’t stopped minimum-wage supporters from attacking the Seattle research. In a June letter to city officials, Mr. Reich, the Berkeley professor, wrote that the study “draws only from areas in Washington State that do not at all resemble Seattle.” But this gives away the game: Any researchers doing this kind of study should explicitly choose control areas that show similar trends, as did the University of Washington team. More to the point, if the controls for Seattle can’t be trusted, it undermines the whole idea of “close comparison.” Criticizing the method only when it delivers evidence against minimum wages suggests the motivations here may be ideological rather than empirical.
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