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Is recruitment more difficult with a placebo arm in RCTs?

BMJ 1999; 319 doi: (Published 25 September 1999) Cite this as: BMJ 1999;319:853

Methodological issues will have affected results

  1. Lindsay Forbes, lecturer in public health medicine (,
  2. Sue Chinn, reader in medical statistics,
  3. Jose Figueroa-Munoz, lecturer in public health medicine,
  4. Paul Seed, lecturer in medical statistics
  1. Department of Public Health Sciences, Guy's, King's and St Thomas's School of Medicine, London SE1 3QD
  2. Medical Research Council Epidemiology and Medical Care Unit, Wolfson Institute of Preventive Medicine, St Bartholomew's and Royal London Hospital School of Medicine and Dentistry, London ECIM 6BQ
  3. Psychology and Genetics Research Group, King's College London, Guy's Campus, London SE1 9RT

    EDITOR—Welton et al found that the proportion of women who were willing to participate in a randomised controlled trial of hormone replacement therapy was higher if participation in a trial without a placebo arm was offered rather than participation in one with a placebo arm, although the difference was of borderline significance.1 Their conclusion was that inclusion of a placebo arm may reduce patients' willingness to participate in a trial. We do not believe that this conclusion is justified.

    Allocation of participants to either of the comparison groups was by the woman's choice of appointment time: the nurses offered participation in trials with and without placebo groups in alternate weeks. This is not random allocation, in which only chance can influence which group a participant is allocated to.2 In this …

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