Opinion: How much does Medicaid improve well-being?

Probably the most controversial thing I've ever written is that the evidence for the effect of health insurance on mortality is not really that strong.  This is not to say that insurance has no effect--this is possible, but not to my mind particularly likely.  But studies purporting to show big impacts are vulnerable to what economists call "unobserved variable bias": because we can't really do massive controlled social experiments on human beings, people who lack health insurance are not exactly like people who have health insurance, except for their health insurance status; they have a bunch of other things going on in their lives that make them less likely to be insured, and which may also affect their health.  (Examples of things that are hard to control for well: they have poor quality social and family networks, have major impulse control problems, have a drinking or drug problem, did not have good parenting, or were born in another, poorer country where they were exposed to disease pathogens and poor nutrition that do not affect American children).