Observational versus randomized trial evidence (Correspondence)

DA Lawlor, G Davey Smith, KR Bruckdorfer, K Tilling, S Ebrahim

Research output: Contribution to journalArticle (Academic Journal)peer-review


Authors' reply When observational epidemiological data and randomised controlled trials produce contradictory findings there is a need to explore the reasons. We showed that the relative risks of mortality from coronary heart disease (CHD) for an identical difference in plasma vitamin C (15·7 μmol/L) suggested a strong beneficial effect in the EPIC observational study1 and weak evidence of possible harm in the Heart Protection randomised controlled trial.2 Heart Protection Study Collaborative Group , MRC/BHF Heart Protection Study of antioxidant vitamin supplementation in 20536 high-risk individuals: a randomised placebo-controlled trial, Lancet 360 (2002), pp. 23–33.2 These differences seem to us to be contradictory rather than consistent. If the observational findings were always clearly explained by factors for ....
Translated title of the contributionObservational versus randomized trial evidence (Correspondence)
Original languageEnglish
Pages (from-to)754 - 755
Number of pages2
Publication statusPublished - Aug 2004

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