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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.

Bongartz , W. , Flammer, E. & Schwonke, R. (2002). Die Effektivität der Hypnose: Eine meta-analytische Studie. Psychotherapeut, 47(2), 67-76.

The ori­ginal pub­lic­a­tion is avail­able on SpringerLink

Flammer, E. & Bongartz, W. (2003). On the Efficacy of Hypnosis: A Meta-Analytic Study. Contemporary Hypnosis, 20(4), 179-197.

The ori­ginal pub­lic­a­tion is avail­able on Whurr publisher’s website

Effect sizes and other study characteristics of 133 studies on the efficacy of hypnosis.

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