Objectives:
The aim of this project was to conduct the cross-cultural factorial validation of the Outcome Questionnaire (OQ-45.2) using the Polish population.

Methods:
Data were obtained from day-patients (n = 211), inpatients (n = 234), outpatients (n = 137) and non-patients (n = 426). Statistical analyses included: parallel analysis, exploratory factor analysis, confirmatory factor analysis, correlation analysis, criterion equivalence, clinical significance and reliable change index, and test-retest.

Results:
Statistical analyses provided the strongest support for the bi-level model of the total score, five orthogonal (subscales specific for the Polish OQ, i.e. Social Conflicts and Addictive Behaviors; and original yet modified subscales, i.e. Symptom Distress, Interpersonal Relations, and Social Role), and two oblique factors (Somatization and Anxiety, Social Role 2). The psychometric properties of the Polish OQ were found to be adequate and similar to the original American OQ and its international adaptations. Specific for the Polish OQ cut-off scores for clinical significance were established. The role of cultural differences and the passage of time in the process of the cross-cultural validation were elaborated upon.

Conclusions:
The Polish version of the OQ 45-2 has been recognized as an instrument adequately measuring general functioning as well as specific areas of functioning of the individual (i.e. interpersonal relations; social role performance; social conflicts; symptom distress; somatization and anxiety; addictive behaviors). Results of this factorial analysis seem to be valuable for both clinicians using the OQ-45.2 and for creators of any psychotherapy outcome measure.