THEORY AND METHODS Population health. More than the sum of the parts?

The past decade has seen an upsurge of interest in the development of summary measures of population health. Almost invariably the measures have relied on ‘‘rolling up’’ individual level health data such as mortality data or life expectancy data. The approach, however, of treating population health as a synthesis of aggregated individual level data is a historical and statistical convenience. Although there has been some debate in the literature about whether one should also examine the equity of the distribution of health, the general practice has been to treat the level of a population’s health and the distribution of health within a population as separate issues. Without recourse to contentious notions of equity, this paper examines the possibility of treating populations as more than simply the sum of their parts by combining individual level health data with population level data about the distribution of health. This approach may provide policy makers with additional ways of thinking about what it means to improve a population’s health.