The evidence is indeed imprecise. Some empirical studies — most famously one published in 1994 in the prestigious American Economic Review by David Card and Alan Krueger — find that on at least some occasions raising the minimum wage might actually increase employment of low-skilled workers. Other studies — for example, this 2004 one by David Neumark and Olena Nizalova — find that the higher the real minimum wage, the worse are the employment prospects of low-skilled workers.

Empirical research in economics is notoriously difficult because wages, prices, unemployment rates, product qualities, and all other data of the social sciences are, as Friedrich Hayek said, "complex phenomena." Having so very much constantly going on in the real world, having no laboratory in which reliably to isolate more than a handful of these phenomena at any one time, and unable to read directly the minds of the many persons whose perceptions and choices combine to generate social outcomes, empirical researchers can easily overlook or misread important variables.