Intended for healthcare professionals

Endgames Statistical Question

Understanding the Hawthorne effect

BMJ 2015; 351 doi: (Published 04 September 2015) Cite this as: BMJ 2015;351:h4672
  1. Philip Sedgwick, reader in medical statistics and medical education1,
  2. Nan Greenwood, associate professor in health and social care service research2
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  2. 2Faculty of Health, Social Care and Education, Kingston University and St George’s, University of London
  1. Correspondence to: P Sedgwick p.sedgwick{at}

Researchers investigated the effectiveness of patient controlled analgesia for patients presenting to emergency departments with pain from traumatic injuries. A randomised controlled trial with a parallel groups study design was used. The control treatment was usual care, with analgesia titrated by nurses according to hospital guidelines. The participants were patients aged 18-75 years presenting to the emergency department who required intravenous opioid analgesia for the treatment of moderate to severe pain resulting from traumatic injuries, and who were expected to be admitted to hospital for at least 12 hours. In total, 200 adults were recruited and randomised to the intervention (patient controlled analgesia; n=99) and control (routine care; n=101) treatment groups.1

The primary outcome was total pain experienced over the 12 hour study period, recorded using a visual analogue scale. Secondary outcomes included total amount of morphine used. The mean total pain experienced by the intervention group was lower than that experienced by the control group, although the difference was not significant. Participants in the intervention group used significantly more morphine than was administered in the usual care group. It was concluded that patient controlled analgesia provided a reduction in pain, albeit not significant, compared with routine care for emergency department patients with traumatic injuries. The researchers commented that the results of the trial may have been influenced by the Hawthorne effect.

Which of the following statements, if any, are true?

  • a) The Hawthorne effect is a change in behaviour as …

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