Worse, the bias introduced by the considerations outlined undermines the authors' conclusions. On every pre-Medicare variable that the authors analyzed, they found that whenever a difference in characteristics was statistically significant, the insured group was healthier than the uninsured group. For instance, the uninsured group was more likely to have smoked, to have impairments in performing activities of daily living, and to be diabetic. It would be surprising if the same were not true for the pertinent unobserved variables as well. Furthermore, preexisting health conditions are often a reason why the near-elderly population cannot obtain health insurance; that is, poor health leads to uninsurance, not the other way around. For these reasons, the difference in Medicare expenditures may only partially reflect a causal effect of insurance on health, and the estimated savings from covering the uninsured might be dramatically overstated.