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).
This is exactly what the study does not find. Indeed, it pretty much confirms what has come to be my view of the evidence on the impact of insurance: you see a very clear impact on utilization, including a handful of recommended preventative screenings, as well as hospitalizations and other treatments. You see a moderately strong effect on both patient and provider finances: fewer medical bills sent to collections, and lower self-reported financial strain from medical costs. And people like being insured, so various self-reported measures rise. The rest is more ambiguous.
For example, the strongest impact on health that they find is that self-reported health status rises by a modest-but-still-significant 0.2 standard deviations: reported depression goes down, while the people who won the lottery were more likely to say that they were in good, very good, or excellent health. This rules out the theory that people who have more contact with the health system might feel less healthy because their doctor gives them more things to be paranoid about, but as Finkelstein et. al note, it doesn't quite show that they're actually healthier. Indeed, about 2/3 of the improvement in self-reported physical health comes almost immediately, before people had a chance to consume much in the way of health services; this suggests that the effect may be psychological rather than the result of any improvement in their physical well being. As the authors say "Overall, the evidence suggests that people feel better off due to insurance, but with the current data it is difficult to determine the fundamental drivers of this improvement."
Meanwhile, while the measures of utilization are strong, the sort of "quality" measures that people often want Medicare to use for reimbursements are considerably less promising:
But death is not that common in the under-65 population, so unless Medicaid has a really large effect on mortality, it's not going to show up in a one-year study. There will be later follow-ups which may give us more suggestive results, of course--and we're running a giant nationwide experiment starting in 2014 which ought to settle the question one way or another. If people really die in the tens of thousands every year because they lack insurance, we should see a noticeable downward inflection in US mortality statistics starting late in this decade.
I think this really points up the difficulty of finding good measures of "health". We can come up with all sorts of objective measures, but we have to keep asking ourselves, relentlessly, whether what we're actually measuring is good or bad: is higher utilization of services really improving peoples' lives? Is lowering easily-measurable blood-cholesterol levels, at the risk of muscle atrophy, an improvement in health, and if so, how much? With some exceptions, the easiest things to measure are not necessarily the most important things to well-being.
This has implications for whether or not we should have a public health plan--is it worth the cost to make people feel happier about their insurance status, or protect them from uncollected medical bills rather than certain death? But it also has implications for how we're going to structure the systems we have. For example, a lot of people are really excited about comparative effectiveness research, which in the public telling, has grown into a painless way to reduce health expenditures by eliminating treatments that don't "work". But while there are some treatments that just shouldn't be done, there's also a large gray area of things that are hard to measure, or to value--extra days of life for a cancer patient, modest reductions in pain or slight increases in mobility, convenience and lifestyle considerations.
And then there's that happiness. As this study shows, we like having access to medical treatment, even if there's no easy-to-measure improvement in our bodies. Paying attention to people, or telling them that a drug will make them feel better, really can make them feel better. What do we do about that? How do we stick that into our equations?
Every time a new study comes out, people on both ends of the political spectrum are quick to seize on it as proof of their prior beliefs. But in this area, the proof is usually messy. It rarely tells us exactly what we wanted--and expected--to hear.