A Cochrane review [Abstract] 1 included 30 studies with a total of 4691 subjects. Median sample size per group was 21. Trials evaluated contracts in addiction (10 trials), hypertension (4 trials), weight control (3 trials) and a variety of other areas (13 trials). Sixteen trials reported at least one outcome that showed statistically significant differences favouring the contracts group, five trials reported at least one outcome that showed differences favouring the control group and 26 trials reported at least one outcome without differences between groups. Effects on adherence were not detected when measured over longer periods.
Comment: The quality of evidence is downgraded by study quality; inadequate allocation concealment and by inconsistency of results; heterogeneity in interventions and outcomes.
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