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

Abstract

The Quality of Life Scale (QLS₂₁) is widely used in clinical trials involving schizophrenia patients. This study aimed to identify a core subset of QLS₂₁ items that maintains the validity and psychometric properties of the complete version. A parsimonious subset of items from the QLS₂₁ 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 QLS₂₁ 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; QLS₅) 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 QLS₅ exhibited similar performance to the QLS₂₁ 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 QLS₅ in routine care and clinical trials may potentially facilitate evaluation of treatment outcomes in schizophrenia.

Introduction

Quality of life measurement has become an established component of mental health outcome assessment. Indeed, there is growing interest in quality of life (QOL) outcomes in studies of treatment response of schizophrenia both in clinical trials and in routine practice (Awad and Voruganti, 2000, Katschnig, 2000, Ritsner and Kurs, 2002, Ritsner and Kurs, 2003). Although satisfaction with QOL is characteristically measured with self-report scales, observer-rated measures such as the Quality of Life Scale (QLS₂₁; Heinrichs et al., 1984) provide useful proxy measures. The QLS₂₁, a 21-item observer-rated scale based on a semistructured interview designed to assess deficit symptoms, is widely used in clinical trials (Hamilton et al., 1999, Kaneda and Ohmori, 2003, Montes et al., 2003, Gureje et al., 2003) and course of illness and rehabilitation studies (Bow-Thomas et al., 1999, Bryson et al., 2002). This scale has acceptable psychometric qualities: test–retest reliability is good for nearly all items of the scale, categories and overall score. Internal consistency alpha coefficients were 0.8–0.9 for the global score, and convergent validity is good (Simon-Abbadi et al., 1999, Kaneda et al., 2002). Cramer et al. (2000) reported that the QLS₂₁ appeared to be substantially more sensitive to subtle change and treatment effects than the patient-report Lehman Quality of Life Interview for clinical trials. The QLS₂₁ assesses four interdependent theoretical constructs: (a) intrapsychic foundations, (b) interpersonal relations, (c) instrumental role functioning, and (d) a two-item construct of common objects and activities that is often incorporated into the construct of intrapsychic foundations. However, the scale items of the QLS₂₁ were derived from consideration of important manifestations of the deficit syndrome in schizophrenia (Heinrichs et al., 1984) and thus have been criticized for reflecting the presence of negative symptoms rather than presenting a clear QOL evaluation (Katschnig, 1997). Indeed, in discussion of the conceptual and methodological requirements for measuring QOL in psychiatry, it has been concluded that there should be a clear distinction between psychopathological symptoms and QOL domains (Katschnig, 1997, Ritsner and Kurs, 2002, Ritsner and Kurs, 2003).

Since QOL studies generally use lengthy questionnaires (ranging from 21 to 143 items), recently several brief versions of QOL instruments were developed and validated (WHOQOL Group, 1998, Lançon et al., 2000, Lobana et al., 2001). Bilker et al. (2003) used a predictive model approach to reduce the number of items collected for scales that yield a total summary score and pioneered a condensed seven-item QOL scale (QLS₇) that included acquaintances, social initiatives, extent, motivation, anhedonia, objects, and empathy. The QLS₇ predicted the QLS₂₁ total summary score with high accuracy (r = 0.98), but, not without considerable drawbacks: the patient sample used to develop the QLS₇ included 31.3% drug-naïve and 32.3% first-episode patients, a sample not representative of the distribution of schizophrenia patients in the general population; the relationship of the QLS₇ to severity of symptoms, side effects, emotional distress, and perceived quality of life was not addressed. In this study we sought to identify a subset of core items from the QLS₂₁ that does not include symptom dimensions and yet maintains the validity of the complete 21-item scale with regard to QOL in long-term schizophrenia patients.