EDITOR, - Trevor A Sheldon's editorial perpetuates the false dichotomy between experimental and observational research.1 Once again an advocate of randomised controlled trials seeks to discredit evaluative research that uses observational data as if the two methods were alternatives rather than complementary approaches. Extremist supporters of either camp offer unacceptably simple accounts.

Of course in some people's ideal world every intervention in the biological and social spheres would be evaluated with a …