Ecologic versus individual-level sources of bias in ecologic estimates of contextual health effects

摘要: A number of authors have attempted to defend ecologic (aggregate) studies by claiming that the goal those is estimation (contextual or group-level) effects rather than individual-level effects. Critics these attempts point out effect estimates are inevitably used as individual effects, despite disclaimers. more subtle problem variation in distribution can bias contextual The conditions leading this plausible and perhaps even common ecosocial factors health outcomes because social context not randomized across typical analysis units (administrative regions). By definition, data contain only marginal observations on joint individually defined confounders outcomes, so identify neither nor While still be useful given appropriate caveats, their problems better addressed multilevel study designs, which obtain use well group-level data. Nonetheless, such often share certain special with studies, including due inappropriate aggregation temporal changes covariate distributions.