Patient's pre-treatment personality characteristics and interpersonal predispositions indicate suitability for psychotherapy and predict its outcome. The predictive value of reliable and valid suitability assessment scales in short- and long-term therapy has not, however, been compared. This study compares the prediction of a suitability scale on changes in psychiatric symptoms in short- and long-term psychotherapy.

In the Helsinki Psychotherapy Study, 326 psychiatric outpatients, aged 20-46 years, and suffering from depressive or anxiety disorders were randomized to short-term therapy or long-term therapy. Psychological suitability measures were assessed with a 7-item Suitability for Psychotherapy Scale (SPS) at baseline and psychiatric symptoms with the Symptom Check List, Global Severity Index (SCL-90-GSI) at baseline and 7 times during a 3-year follow-up.

Three patient groups were found when a suitability score based on the seven individual suitability measures was used to predict symptom development: patients with more good (4 or more) than poor values gained sufficiently from short-term therapy, patients with more poor (4-6) than good values needed long-term therapy, and patients with all 7 values poor failed to benefit from either short- or long-term therapy. Almost half of the patients received considerably auxiliary treatment besides the study treatment. For these patients, although equipped with mostly good values, short-term therapy was not sufficient.

The amount of therapy needed to recover may be predicted before start of therapy. The use of auxiliary treatment in addition to standard treatment needs, however, further clarification.