Condensed version of the Quality of Life Scale for schizophrenia for use in outcome studies

Abstract

The Quality of Life Scale (QLS 21) is widely used in clinical trials involving schizophrenia patients. This study aimed to identify a core subset of QLS 21 items that maintains the validity and psychometric properties of the complete version. A parsimonious subset of items from the QLS 21 that can accurately predict the total scale score was sought and evaluated in 133 schizophrenia patients, using the heuristic algorithm for a regression model. Two additional data sets were used for model validation: a subset of 124 patients who participated in the model construction and who completed the QLS 21 1 year later as well as a new sample of 40 inpatients. Patients were examined with the Positive and Negative Syndrome Scale (PANSS), the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q), the Talbieh Brief Distress Inventory (TBDI), the Extrapyramidal Symptom Rating Scale (ESRS) and the Global Assessment of Functioning Scale (GAF). Using only five QLS items (social initiatives, adequacy, acquaintances, motivation, and time utilization; QLS 5) as predictors, the correlation was 0.9805 between the predicted and true QLS totals. Two validation samples confirmed this finding. Additional analyses indicate that the QLS 5 exhibited similar performance to the QLS 21 regarding construct validity, test–retest reliability and responsiveness to changes over time. Thus, the five-item condensed Quality of Life Scale for schizophrenia maintains the validity of the full QLS, and has the advantage of shorter administration time. Utilization of the revised QLS 5 in routine care and clinical trials may potentially facilitate evaluation of treatment outcomes in schizophrenia.