After you make history, it only makes sense that you'd want that history to be accurate. That's why after passing the nation's first citywide $15 minimum wage law, the City of Seattle contracted with some top researchers from the University of Washington to conduct a deep multi-year study of the economic impacts of the law on prices, employment, low-wage workers, and the economy as a whole.
A first initial report is in, and after some comprehensive data-gathering, here's what they have found:
"Results, derived from repeated price collection in a range of retail outlets including grocery stores, drugstores, and small businesses, show no significant impact of the minimum wage ordinance on price levels"
Their methodology included walking door to door collecting prices, GrubHub data, and more. The only price increases of any kind they have detected were at restaurants... and restaurant prices increased almost exactly the same amount outside the city. In order words: so far, there's effectively zero price impact from the first phase-in towards $15.
The entire early report from their research project [PDF] is fascinating if you've got a hankering for interesting methodology. We look forward to hearing more from the first complete report, due to Seattle City Council in June.