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‘Placebos’ and the logic of placebo comparison

Abstract

Robin Nunn has argued that we should stop using the terms ‘placebo’ and ‘placebo effect’. I argue in support of Nunn’s position by considering the logic of why we perform placebo comparisons. Like all comparisons, placebo comparison is just a case of comparing one thing with another, but it is a mistake, I argue, to think of placebo comparison as a case where something is compared to ‘a placebo’. Rather, placebo comparison should be understood as a situation which sets-up the treatment and control groups in a particular way; not as a case involving objects or procedures called ‘placebos’ employed in order to control for ‘placebo effects’.

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Notes

  1. 1.

    The concern in this paper is with placebo comparison, and so the argument is about the use of the term ‘placebo’ in a research context. Clearly however, the term has uses in clinical contexts that may be valid for independent reasons. I would expect the argument made here to apply to the clinical context; since the general idea is simply that the term obscures what can be better explained in more precise terms. However I will not argue explicitly for this here.

  2. 2.

    Although note that such a principle does not imply that we cannot know that a treatment is efficacious unless a placebo comparison has been performed. It simply equates efficacious treatments with placebo outperforming treatments. If we know a treatment is efficacious, that justifies the belief that it would outperform placebo, were such a comparison to be performed.

  3. 3.

    Or more precisely, a pill with no therapeutically relevant contents (cf. Golomb 1995; Golomb et al. 2010).

  4. 4.

    Actually I’m just assuming they were sugar pills. We are told in the Branthwaite & Cooper’s methods section (1981, p. 1576) that the pills not containing aspirin were the same size, shape, weight and colour, and that they were not designed to taste the same as aspirin tablets. The content of these pills is not disclosed.

  5. 5.

    Note aside that only some aspects of a treatment can be controlled for by randomisation (if that is, any can. See: Worrall 2007, 2010). In practice randomisation and the subsequent adjustment of baseline imbalances helps to minimise, for example, the influence of patients’ differing expectations. However even in the ideal case randomisation would not help at all to solve the problem of treatment groups that were under the supervision of ‘nasty doctor’ on the one hand and ‘nice doctor’ on the other. The attitude and behaviour of the treating physician is something that we must seek to homogenise between groups through other means.

  6. 6.

    Use of the term ‘placebo’ could also be important in a different way, if that usage created therapeutically relevant expectations in a patient. For example in a clinical context, through being told one is receiving ‘a placebo’; or in a research context, through being enrolled in a trial and told that one may be randomised to a placebo group. See for example: Kaptchuk et al. (2010) and Enck et al. (2011).

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Acknowledgments

Thanks to those at the 2010 ‘Progress in Medicine’ conference in Bristol who offered comments on a very early version of this paper, and thanks to Robin Nunn for comments on a much more recent version. Thanks also to the helpful comments of the anonymous reviewers.

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Correspondence to Andrew Turner.

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Turner, A. ‘Placebos’ and the logic of placebo comparison. Biol Philos 27, 419–432 (2012). https://doi.org/10.1007/s10539-011-9289-8

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Keywords

  • Placebo
  • Placebo controlled trial
  • Clinical trials
  • Evidence-based medicine