• Incineration
• congenital abnormalities
• air pollution
• causality
• primary prevention
• epidemiology
• congenital anomalies
• genito-urinary
• dioxins

A paper in this issue of Occupational and Environmental Medicine (see page 493) provides evidence that exposure to emissions from municipal solid waste incinerators (MSWIs) increases the risk of urinary tract birth defects.1 These findings raise concern of potentially large health impacts, given the widespread and growing use of this technology. But epidemiologists have learned to interpret any single study, no matter how compelling, with caution and nuance. They will ask: how valid was the exposure model? How serious was the selection bias resulting from inability to interview 38% of the cases? To what extent was the potential confounding by social class variables effectively controlled? Rather than providing my own judgements about these and other questions concerning this study's validity, I would like to address some brief remarks to non-experts who may find Cordier's study and wonder how much weight to give it as they form their own opinions about the health impacts of MSWIs.

It is often argued that science should be kept distinct from policy; scientists should conduct their research without prejudice or influence, and should be responsible only for providing data to policymakers or the public. …