Bmj Usa: Editor's Choice

The randomized trial on its pedestal

BMJ 2003; 327 doi: (Published 19 November 2003) Cite this as: BMJ 2003;327:E137

From BMJ USA 2002;September:477

The news about hormone replacement reminds us of the distinction between observational and randomized data. Treatments that seem promising in observational studies are often refuted in randomized trials. The comparison groups in observational studies often differ in characteristics other than the intervention of interest. Observational evidence linking coffee with pancreatic cancer has less to do with coffee than with the frequency with which coffee drinkers smoke. Randomized trials distribute confounding variables equally, making it safer to conclude that differences across groups reflect the intervention in question.

For years doctors forgot this principle in assuming, largely from observational data, that hormone replacement prevents heart disease. Skeptics wondered whether health habits or other …

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