It is incredibly difficult to experiment in economics because you can't control for a single variable. If I like minimum wage, I'll look for employment data during a boom to mask the negative effects. If I dislike it, I'll look for data during a bust. That's over simplifying, but it is why we have multiple studies both showing minimum wage helped and hurt.
Dube, Lester, Reich did a study that accounted for booms and busts by looking at a series of minimum wage increases across state borders between 1990 and the present.
