Allocation concealment  and blinding: when  ignorance is bliss

Hemilä, Harri

doi:10.5694/j.1326-5377.2005.tb06975.x

Topics

Statistics, epidemiology and research design

To the Editor: In their article on controlled trials, Forder et al1 described the trial by Karlowski et al on vitamin C and the common cold2 as an example of how patients’ or investigators’ preconceptions about the value of the treatment may affect a trial’s results. However, their presentation of this trial is misleading in two respects.

Department of Public Health, University of Helsinki, POB 41, Helsinki, FIN-00014, Finland.

Correspondence: harri.hemila@helsinki.fi

1. Forder PM, Gebski VJ, Keech AC. Allocation concealment and blinding: when ignorance is bliss. Med J Aust 2005; 182: 87-89. <MJA full text>
2. Karlowski TR, Chalmers TC, Frenkel LD, et al. Ascorbic acid for the common cold: a prophylactic and therapeutic trial. JAMA 1975; 231: 1038-1042.
3. Hemilä H. Vitamin C, the placebo effect, and the common cold: a case study of how preconceptions influence the analysis of results. J Clin Epidemiol 1996; 49: 1079-1084; discussion in 1085-1087.
4. Beecher HK. The powerful placebo. JAMA 1955; 159: 1602-1606.
5. Hrobjartsson A, Gøtzsche PC. Is the placebo powerless? An analysis of clinical trials comparing placebo with no treatment. N Engl J Med 2001; 344: 1594-1602; discussion in 2001; 345: 1276-1279.
6. Douglas RM, Hemilä H, D’Souza R, et al. Vitamin C for preventing and treating the common cold (Cochrane Review). In: The Cochrane Library, Issue 4, 2004. Abstract available at: http://www.cochrane.org/cochrane/revabstr/AB000980.htm (accessed Apr 2005).

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