Needed: Global Collaboration for Comparative Research on Cities and Health.

Over half of the world's population lives in cities and United Nations (UN) demographers project an increase of 2.5 billion more urban dwellers by 2050. Yet there is too little systematic comparative research on the practice of urban health policy and management (HPAM), particularly in the megacities of middle-income and developing nations. We make a case for creating a global database on cities, population health and healthcare systems. The expenses involved in data collection would be difficult to justify without some review of previous work, some agreement on indicators worth measuring, conceptual and methodological considerations to guide the construction of the global database, and a set of research questions and hypotheses to test. We, therefore, address these issues in a manner that we hope will stimulate further discussion and collaboration.