In the context of responding to an article in The Atlantic by Megan McArdle, J. Michael McWilliams does a good job of laying out some of the statistical problems that underlie attempts to measure things such as the effectiveness of insurance in health outcomes. For example:
From the quasi-experimental literature, McArdle cites evidence of a lack of immediate survival gains with near-universal Medicare coverage after age 65 in the general population (Card et al. 2004; Levy, and Meltzer 2008). From a clinical perspective, however, we should not expect immediate survival gains for most previously uninsured adults because mortality is such a distal outcome. Survival gains may not manifest for years after improved chronic disease control and cancer screening are established, suggesting much more complex improvements in mortality trends are likely to evolve after age 65 in response to universal coverage. Quasi-experiments that rely on abrupt discontinuities occurring with age are not well suited to capturing these complex but potentially large effects. Consequently, the absence of evidence suggested by these studies is not evidence of absence. In contrast to the general population, immediate mortality effects might be expected for acutely ill patients for whom coverage may improve access to life-saving procedures and therapies.
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