The evaluation of a psychotherapeutic method - like hypnotherapy -is achieved, usually, by conducting a meta-analysis of the relevant clinical studies. The meta-analytic procedure results in so-called effect-sizes that are computed for each clinical study. An effect-size for a given clinical study is estimated either from the standardized difference (using the pooled standard deviation , for instance) between the mean values (e.g., anxiety scores) for a treated and an untreated group of patients or from the difference between the mean values before and after treatment (pre-post measurement). These measures allow direct comparisons between studies regarding their efficacy. Frequently used measures for effect-sizes are standardized mean differences or correlation coefficients. Effect-sizes standardized mean differences) from d=.2 to d=.5 indicate weak/low efficacy, effect-sizes from d=.5 to d=.8 average efficacy of a therapy; at d=.8 psychotherapies are (regarded as having good up to very good efficacy.
We have carried out a meta-analysis on the efficacy of hypnosis taking into consideration 133 clinical studies between 1974 and 2002. For detailed information on our study see our article.
The original publication is available on SpringerLink
The original publication is available on Whurr publisher’s website