The Scandinavian welfare regime is expected to have better aggregate health than other welfare regimes due mainly to its narrow income inequality. This theoretical expectation is in part related to the Wilkinson Hypothesis that, in industrialised nations, a society’s narrow income inequality enhances its aggregate health. This thesis tests both of the above propositions. This is achieved by means of four methods not previously applied to this field, namely a ‘review of reviews’, a decomposition systematic review, a new case selection method, and a use of the OECD regional dataset for the cross-national comparative health study. These new methodological approaches lead to four main findings. First, the Scandinavian welfare regime shows worse-than-expected aggregate health outcomes. This thesis terms this counterintuitive finding as ‘the second Scandinavian puzzle’. Second, the East Asian welfare regime shows unexpectedly good aggregate health, which is proposed as ‘the East Asian puzzle’. Third, regarding the Wilkinson Hypothesis, it is income, rather than income inequality, which is a statistically significant determinant of aggregate health. Fourth, the effects on health of income inequality or welfare regimes reverse over a certain threshold of age, which is termed here ‘the age threshold effect’.