title: Ecological studies: use with caution.
authors.affiliation: University of Cambridge, Cambridge Centre for Health Services Research, Institute of Public Health, Cambridge.
authors.forename: Catherine
authors.initials: C
authors.lastname: Saunders
authors.forename: Gary
authors.initials: G
authors.lastname: Abel
mesh_terms: D002986:Clinical Trials as Topic; D003625:Data Collection; D055669:Ecological and Environmental Phenomena; D006801:Humans; D011320:Primary Health Care; D012107:Research Design; D013222:State Medicine / Q000458:organization & administration