Don C. Brunell

Washington has the nation’s highest minimum wage at $9.47 an hour and now the state legislature wants to hike it to $12. Seattle Mayor Ed Murray (D) wants to boost it to $15 to go in step with the SeaTac initiative, which voters barely approved last year. The state’s minimum wage has been adjusted annually since 2001, based on a Seattle-area cost of living index.

From 2008 through 2013, Washington’s minimum wage increased more than 14%. Washington voters thought passing an initiative 14 years ago would make life better for the poor and low income families, but has it?

Stanford economics profes...