Placebo interventions are often believed to improve patient reported and observer reported outcomes, but this belief is not based on evidence from randomised trials that compare placebo with no treatment.
To assess the effect of placebo interventions.
We searched the Cochrane Controlled Trials Register (The Cochrane Library, issue 3, 1998), MEDLINE (Jan 1966 to Dec 1998), EMBASE (Jan 1980 to Dec 1998), Biological Abstracts (Jan 1986 to Dec 1998), PsycLIT (Jan 1887 to Dec 1998). Experts on placebo research were contacted and references in the included trials were read.
Randomised placebo trials with a no-treatment control group investigating any health problem were included.
Two reviewers independently assessed trial quality and extracted data. Study authors were contacted for additional information.
Outcome data were available in 114 out of 130 included trials, investigating 40 clinical conditions. Outcomes were binary in 32 trials (3795 patients) and continuous in 82 (4730 patients). We found no statistically significant pooled effect of placebo in studies with binary outcomes, relative risk 0.95 (95 per cent confidence interval 0.88 to 1.02). The pooled relative risk for subjective (patient reported) outcomes was 0.95 (0.86 to 1.05) and for objective (observer reported) outcomes 0.91 (0.80 to 1.04). There was statistically significant heterogeneity (P < 0.03), but no evidence of sample size bias (P = 0.56). We found an overall positive effect of placebo treatments in trials with continuous outcomes, standardised mean difference -0.28 (95 per cent confidence interval -0.38 to -0.19). The standardised mean difference for subjective outcomes was -0.36 (-0.47 to -0.25), whereas no statistically significant effect was found for objective outcomes, standardised mean difference -0.12 (-0.27 to 0.03). There was statistically significant heterogeneity (P < 0.001), and evidence of sample size bias (P = 0.05). There was no statistically significant effect of placebo interventions in eight out of nine clinical conditions investigated in three trials or more (nausea, relapse in prevention of smoking and depression, overweight, asthma, hypertension, insomnia and anxiety), but confidence intervals were wide. There was a modest apparent analgesic effect of placebo interventions, standardised mean difference -0.27 (-0.40 to -0.15), but also a substantial risk of bias.
There was no evidence that placebo interventions in general have clinically important effects. A possible moderate effect on subjective continuous outcomes, especially pain, could not be clearly distinguished from bias.
"The purpose of this study was to assess the relationship of participants' beliefs about drug assignment to abstinence status in two treatment studies using nortriptyline hydrochloride. Blinding is a cornerstone of randomized clinical trials in drug evaluation (Fergusson, Glass, Waring, & Shapiro, 2004; Gaudino & Herbert, 2005; Hrobjartsson & Gotzsche, 2003, 2004). Studies of pharmacotherapies for tobacco dependence have adhered to this tradition. "
[Show abstract][Hide abstract] ABSTRACT: This study assessed the relationship between beliefs about drug assignment and abstinence status in two treatment studies using nortriptyline hydrochloride as an adjunct to smoking cessation. Smokers (N = 345) drawn from two clinical trials were asked at the final follow-up (FFU) at 52 or 64 weeks whether they believed they had received active or placebo drug. Responses were obtained from 262 participants, or 76% of the sample. Biochemically verified abstinence was collected at end of treatment (EOT) and FFU. In both studies, participants were correct in guessing drug assignment. At FFU, belief about drug assignment was not related to abstinence for either active or placebo participants. Participants who received active drug and who were smoking at EOT were more likely to believe they had received placebo than active drug participants who were abstinent at EOT. We found no significant relationship between belief about drug and abstinence status for placebo participants at EOT. Baseline variables did not significantly predict correctness of drug identification. Participants who experienced drug side-effects not easily attributable to nicotine withdrawal were more likely to identify their drug assignment as nortriptyline. We conclude that experience during the active treatment period, including side-effects and treatment success, may be related to belief about drug assignment, that the field would be well served by at least two assessments of blindness in clinical trials, and that discrepancy between these findings and those regarding nicotine replacement therapy may be related to differences in dependent variables.
[Show abstract][Hide abstract] ABSTRACT: Assessing the quality of an epidemiological study equates to assessing whether the inferences drawn from it are warranted when account is taken of the methods, the representativeness of the study sample, and the nature of the population from which it is drawn. Bias, confounding, and chance can threaten the quality of an epidemiological study at all its phases. Nevertheless, their presence does not necessarily imply that a study should be disregarded. The reader must first balance any of these threats or missing information with their potential impact on the conclusions of the report.
Postgraduate Medical Journal 04/2004; 80(941):140-7. DOI:10.1136/pgmj.2003.012633 · 1.45 Impact Factor
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