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Open Access Highly Accessed Research article

The Hawthorne Effect: a randomised, controlled trial

Rob McCarney1, James Warner1*, Steve Iliffe2, Robbert van Haselen3, Mark Griffin2 and Peter Fisher4

Author Affiliations

1 Department of Psychological Medicine, Imperial College London, UK

2 Department of Primary Care and Population Sciences, University College London, UK

3 International Institute for Integrated Medicine, France

4 Royal London Homœopathic Hospital, London UK

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BMC Medical Research Methodology 2007, 7:30  doi:10.1186/1471-2288-7-30

Published: 3 July 2007

Abstract

Background

The 'Hawthorne Effect' may be an important factor affecting the generalisability of clinical research to routine practice, but has been little studied. Hawthorne Effects have been reported in previous clinical trials in dementia but to our knowledge, no attempt has been made to quantify them. Our aim was to compare minimal follow-up to intensive follow-up in participants in a placebo controlled trial of Ginkgo biloba for treating mild-moderate dementia.

Methods

Participants in a dementia trial were randomised to intensive follow-up (with comprehensive assessment visits at baseline and two, four and six months post randomisation) or minimal follow-up (with an abbreviated assessment at baseline and a full assessment at six months). Our primary outcomes were cognitive functioning (ADAS-Cog) and participant and carer-rated quality of life (QOL-AD).

Results

We recruited 176 participants, mainly through general practices. The main analysis was based on Intention to treat (ITT), with available data. In the ANCOVA model with baseline score as a co-variate, follow-up group had a significant effect on outcome at six months on the ADAS-Cog score (n = 140; mean difference = -2.018; 95%CI -3.914, -0.121; p = 0.037 favouring the intensive follow-up group), and on participant-rated quality of life score (n = 142; mean difference = -1.382; 95%CI -2.642, -0.122; p = 0.032 favouring minimal follow-up group). There was no significant difference on carer quality of life.

Conclusion

We found that more intensive follow-up of individuals in a placebo-controlled clinical trial of Ginkgo biloba for treating mild-moderate dementia resulted in a better outcome than minimal follow-up, as measured by their cognitive functioning.

Trial registration

Current controlled trials: ISRCTN45577048