Validation of the Illness Perception Questionnaire for Schizophrenia in a German-speaking sample of outpatients with chronic schizophrenia.

BACKGROUND

Because the mere definition of insight from the therapist's viewpoint may not be sufficient to identify treatment targets for adherence enhancement, we need assessment strategies which are more sensitive to the patient's perspective. Illness perception (IP), defined as the beliefs a patient holds about his/her health problems, has been shown to affect coping in the context of a physical or mental illness, e.g. compliance behaviour. To assess IP in people diagnosed with schizophrenia, the Illness Perception Questionnaire for Schizophrenia (IPQS) was developed. The aim of the present study was to analyse the psychometric properties of the German version of the IPQS.

SAMPLING AND METHODS

The study sample consisted of 128 German-speaking outpatients suffering from chronic schizophrenia or schizoaffective disorder. To achieve comparability with the validation of the English scale version, the same constructs were assessed: psychopathology, depression, and beliefs about medication. Furthermore, insight into one's illness was assessed. Internal consistency, test-retest reliability and construct validity including convergent and discriminant validity were analysed.

RESULTS

Five of eight IPQS subscales were found to be internally reliable and all subscales demonstrated high stability over time. Correlations with validity measures indicated that the subscales assess dimensions of a construct, which is distinct from psychopathology, depression, beliefs about medication and insight, except for the Identity subscale which substantially overlapped with measures of insight.

CONCLUSIONS

The German version of the IPQS is an essentially reliable and valid measure of IP for German-speaking people with a schizophrenia spectrum disorder. This may encourage its usage in further studies investigating the impact of subjective beliefs about mental health problems on outcome and recovery in schizophrenia.