Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Randomized Controlled Trial
, 7, 30

The Hawthorne Effect: A Randomised, Controlled Trial

Randomized Controlled Trial

The Hawthorne Effect: A Randomised, Controlled Trial

Rob McCarney et al. BMC Med Res Methodol.


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.


Figure 1
Figure 1
Participant flowchart.

Similar articles

See all similar articles

Cited by 285 PubMed Central articles

See all "Cited by" articles


    1. Mayo E. The human problems of an industrial civilization. 2. Vol. 3. New York, MacMillan; 1993. pp. 53–73.
    1. Roethlisberger FJ, Dickson WJ. Management and the Worker. Cambridge, Mass., Harvard University Press; 1939.
    1. Franke RH, Kaul JD. The Hawthorne experiments: First statistical interpretation. Am Sociol Rev. 1978;43:623–643. doi: 10.2307/2094540. - DOI
    1. Braunholtz DA, Edwards SJ, Lilford RJ. Are randomized clinical trials good for us (in the short term)? Evidence for a "trial effect". [Review] [26 refs] Journal of Clinical Epidemiology. 2001;54:217–224. doi: 10.1016/S0895-4356(00)00305-X. - DOI - PubMed
    1. Peppercorn JM, Weeks JC, Cook EF, Joffe S. Comparison of outcomes in cancer patients treated within and outside clinical trials: conceptual framework and structured review.[see comment]. [Review] [52 refs] Lancet. 2004;363:263–270. doi: 10.1016/S0140-6736(03)15383-4. - DOI - PubMed

Publication types

MeSH terms

Associated data