title: Linking exercise and outcomes: difficulties of study design.
authors.forename: C M
authors.initials: CM
authors.lastname: Kozma
mesh_terms: D000368:Aged; D015444:Exercise; D006305:Health Status Indicators; D006801:Humans; D017063:Outcome Assessment, Health Care; D011897:Random Allocation; D012107:Research Design; D014481:United States / Q000453:epidemiology