Problems of process-efficiency studies in psychotherapy.

Three areas of psychotherapy research can be delimited of which differential efficiency research promises to be the most fruitful, because it will eventually inform us which interventions with what kind of patient and what kind of problem will be the most constructive. One problem it can solve is the so-called equivalence paradox. This epitheton designates the fact, that in spite of the enormous differences in theory and interventions between the different kinds of psychotherapies, their results are not remarkably divergent. One quite popular hypothesis is that this is due to common factors, commun to any and every kind of psychotherapy. Our results indicate that this explanation is too simplistic because it uses a monosubstance-doses-effect-relationship model and disregards interaction. One other avenue is the relevant events approach. Our examples yield equivocal results. Nevertheless this remains a promising field of investigation. Finally there are time series analyses which are probably most germane to the field of psychotherapies. One illustration with a case of negative psychotherapy outcome is presented. Time series analysis is able to show that the patient changed to a negativistic attitude in the middle of session, whereas the psychoanalyst only changed at the beginning of session 10 respectively in its middle.