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J Clin Epidemiol. 2011 Nov;64(11):1223-9. doi: 10.1016/j.jclinepi.2011.01.008. Epub 2011 Apr 23.

Placebo effect studies are susceptible to response bias and to other types of biases.

Author information

1
The Nordic Cochrane Centre, Rigshospitalet, Copenhagen, Denmark. ah@cochrane.dk

Abstract

OBJECTIVE:

Investigations of the effect of placebo are often challenging to conduct and interpret. The history of placebo shows that assessment of its clinical significance has a real potential to be biased. We analyze and discuss typical types of bias in studies on placebo.

STUDY DESIGN AND SETTING:

A methodological analysis and discussion.

RESULTS:

The inherent nonblinded comparison between placebo and no-treatment is the best research design we have in estimating effects of placebo, both in a clinical and in an experimental setting, but the difference between placebo and no-treatment remains an approximate and fairly crude reflection of the true effect of placebo interventions. A main problem is response bias in trials with outcomes that are based on patients' reports. Other biases involve differential co-intervention and patient dropouts, publication bias, and outcome reporting bias. Furthermore, extrapolation of results to a clinical settings are challenging because of a lack of clear identification of the causal factors in many clinical trials, and the nonclinical setting and short duration of most laboratory experiments.

CONCLUSIONS:

Creative experimental efforts are needed to assess rigorously the clinical significance of placebo interventions and investigate the component elements that may contribute to the therapeutic benefit.

PMID:
21524568
PMCID:
PMC3146959
DOI:
10.1016/j.jclinepi.2011.01.008
[Indexed for MEDLINE]
Free PMC Article

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