The University of Washington researchers looked at a more detailed pool of data than some minimum-wage researchers before them, combing through numbers collected for the local unemployment-insurance program. When compared to data from other parts of Washington state, which represented a similar economy with no minimum-wage hikes, these numbers indicated that the hike had a major effect. The number of jobs paying less than $13 an hour dropped by 39 percent, they found, with the number of jobs paying less than $19 an hour falling by a smaller amount. At the same time, overall employment in Seattle increased by 13 percent, judging by headcount, and 15 percent, judging by hours. But many low-wage workers suffered from hours, job, and earnings losses. The wage hike pulled the bottom rung off of the ladder, in other words.

The study contradicts a paper put out last week by respected researchers at the University of California, Berkeley. It found that Seattle’s minimum wage boosted wages by roughly 1 percent in food services overall and 2.3 percent in limited-service restaurants, like fast-food chains, with little effect on employment. “This industry is an intense user of minimum wage workers,” the authors write. “If wage and employment effects occur, they should be detectable in this industry.” A body of other studies dating back for more than 20 years have found similar effects: Most wage hikes do not do much to change employment levels.

Given the University of Washington’s diverging results, researchers on the left argued for caution in interpreting them and applying them to policymaking. “The authors’ estimated employment effects stand as outliers in a large body of research on the employment effects of the minimum wage,” wrote Ben Zipperer and John Schmitt of the Economic Policy Institute, a left-of-center think tank based in Washington, D.C. “Rather than constituting an important new contribution to the research in this area, the findings are best seen as raising concerns about possible problems with their underlying data and statistical techniques.”

The University of Washington study excluded workers at companies with multiple locations—meaning McDonald’s, Starbucks, and the other big and small chains that account for about 40 percent of the overall workforce and a huge number of minimum-wage jobs—narrowing the scope of the results, Zipperer and Schmitt noted. The study also seemed to imply that the minimum-wage hike caused a boom in high-wage employment, a seemingly impossible feat. (It seems unlikely that a business would have reacted to a pay hike for a minimum-wage worker by paying many of them $19 an hour, after all.) It in addition had no way to tell if Seattle’s employers were switching to contractors, as opposed to employees, to avoid some provisions of the minimum-wage law; if that had happened, those workers would have dropped out of the data set.