Unlike most opponents of the minimum wage, I admit that David Card and Alan Krueger's famous research on the topic is well-done. How then can I continue to embrace (and teach!) the textbook view that the minimum wage significantly reduces employment of low-skilled workers?
Part of the reason is admittedly my strong prior. In the absence of any specific empirical evidence, I am 99%+ sure that a randomly selected demand curve will have a negative slope. I hew to this prior even in cases - like demand for illegal drugs or illegal immigration - where a downward-sloping demand curve is ideologically inconvenient for me. What makes me so sure? Every purchase I've ever made or considered - and every conversation I've had with other people about every purchase they've ever made or considered.
Another reason why Card-Krueger hasn't flipped my position: Despite my admiration for their craftsmanship, even the best empirical social science isn't that good. I expect true theories to predict the data only two-thirds of the time - and false theories to predict the data one-third of the time. (N.B. Many of the weaknesses in empirical social science are systematic, so the Law of Large Numbers is no salvation). Bayesian upshot: The Card-Krueger findings only slightly reduce my initial high confidence that the minimum wage causes unemployment.
But suppose you disagree with me on both counts. Suppose you have a weak prior about the disemployment effects of the minimum wage. Suppose further that you think that the best empirical work in economics is very good indeed. Doesn't existing evidence then oblige you to admit that the minimum wage has roughly zero effect on employment?
Hardly. Why not? Because there is far more "existing evidence" than meets the eye. Research doesn't have to officially be about the minimum wage to be highly relevant to the debate. All of the following empirical literatures support the orthodox view that the minimum wage has pronounced disemployment effects:
1. The literature on the effect of low-skilled immigration on native wages. A strong consensus finds that large increases in low-skilled immigration have little effect on low-skilled native wages. David Card himself is a major contributor here, most famously for his study of the Mariel boatlift. These results imply a highly elastic demand curve for low-skilled labor, which in turn implies a large disemployment effect of the minimum wage.
This consensus among immigration researchers is so strong that George Borjas titled his dissenting paper "The Labor Demand Curve Is Downward Sloping." If this were a paper on the minimum wage, readers would assume Borjas was arguing that the labor demand curve is downward-sloping rather than vertical. Since he's writing about immigration, however, he's actually claiming the labor demand curve is downward-sloping rather than horizontal!
2. The literature on the effect of European labor market regulation. Most economists who study European labor markets admit that strict labor market regulations are an important cause of high long-term unemployment. When I ask random European economists, they tell me, "The economics is clear; the problem is politics," meaning that European governments are afraid to embrace the deregulation they know they need to restore full employment. To be fair, high minimum wages are only one facet of European labor market regulation. But if you find that one kind of regulation that raises labor costs reduces employment, the reasonable inference to draw is that any regulation that raises labor costs has similar effects - including, of course, the minimum wage.
3. The literature on the effects of price controls in general. There are vast empirical literatures studying the effects of price controls of housing (rent control), agriculture (price supports), energy (oil and gas price controls), banking (Regulation Q) etc. Each of these literatures bolsters the textbook story about the effect of price controls - and therefore ipso facto bolsters the textbook story about the effect of price controls in the labor market.
If you object, "Evidence on rent control is only relevant for housing markets, not labor markets," I'll retort, "In that case, evidence on the minimum wage in New Jersey and Pennsylvania in the 1990s is only relevant for those two states during that decade." My point: If you can't generalize empirical results from one market to another, you can't generalize empirical results from one state to another, or one era to another. And if that's what you think, empirical work is a waste of time.
4. The literature on Keynesian macroeconomics. If you're even mildly Keynesian, you know that downward nominal wage rigidity occasionally leads to lots of involuntary unemployment. If, like most Keynesians, you think that your view is backed by overwhelming empirical evidence, I have a challenge for you: Explain why market-driven downward nominal wage rigidity leads to unemployment without implying that a government-imposed minimum wage leads to unemployment. The challenge is tough because the whole point of the minimum wage is to intensify what Keynesians correctly see as the fundamental cause of unemployment: The failure of nominal wages to fall until the market clears.
The minimum wage is far from the most harmful regulation on the books. Why then do I make such a big deal about it? Because it is a symbol of larger evils.
From the standpoint of public policy, the minimum wage is a symbol of the view that "feel-good" policies are viable solutions to social ills: "Workers aren't paid enough? Pass a law so employers have to pay them more. Problem solved." From the standpoint of social science, the minimum wage is a symbol of the myopic view that you can become an expert on X by reading nothing but the leading research that explicitly addresses X: "Does the minimum wage reduce employment? Read the top papers on the minimum wage. Problem solved."
We need to get rid of the minimum wage. But that's only a first step. Our ultimate goal should be to get rid of the errors that the minimum wage has come to represent.