Paper
Hypnotic enhancement of cognitive-behavioral weight loss treatments--another meta-reanalysis.
Published 1996 · Irving Kirsch
Journal of Consulting and Clinical Psychology
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Abstract
In a 3rd meta-analysis of the effect of adding hypnosis to cognitive-behavioral treatments for weight reduction, additional data were obtained from authors of 2 studies, and computational inaccuracies in both previous meta-analyses were corrected. Averaged across posttreatment and follow-up assessment periods, the mean weight loss was 6.00 Ibs. (2.72 kg) without hypnosis and 11.83 Ibs. (5.37 kg) with hypnosis. The mean effect size of this difference was 0.66 SD. At the last assessment period, the mean weight loss was 6.03 Ibs. (2.74 kg) without hypnosis and 14.88 Ibs. (6.75 kg) with hypnosis. The effect size for this difference was 0.98 SD. Correlational analyses indicated that the benefits of hypnosis increased substantially over time (r = .74). Meta-analyses allow comparisons of outcomes among studies using different instruments to measure dependent variables. By standardizing scores, the effects of psychotherapy (Smith, Glass, & Miller, 1980) or of the addition of particular therapeutic procedures to therapy (Kirsch, Montgomery, & Sapirstein, 1995) can be assessed across a wide range of presenting problems. Even in studies assessing treatment effects on the same presenting problem (e.g., depression), the use of different measuring instruments may require the calculation of standardized effect sizes. The studies comparing weight reduction treatments with and without hypnosis present less of a problem. Weight loss in pounds or kilograms were reported in each of them. Because they used a common dependent measure, their results can be examined directly without having to decide what assumptions should be made in estimating unreported parameters.1 The mean weight loss in hypnotic treatments, nonhypnotic treatments, and the difference in mean weight loss between these two forms of treatment are presented in Table 1.2 Across all assessment periods, these data indicate a mean weight loss of 6.00 Ibs. (2.72 kg) without hypnosis and 11.83 Ibs. (5.37 kg) with hypnosis. Thus, including hypnosis in the treatment protocol resulted in an additional loss of 5.83 Ibs. (2.64 kg), a 97% increase in treatment efficacy.
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