[Development and validation of a self rating quality of life scale: the S-QoL]

Abstract

Introduction: Evaluation of subjective quality of life in schizophrenia is a recent phenomenon. Few subjective quality of life questionnaires are available and validated, especially in French. Most of the available scales are hetero questionnaires based on experts' opinion. We describe the development and the validation of a new self-rating questionnaire of quality of life for schizophrenic patients, the S-QoL. The S-QoL was based on Calman's approach to the subject's point of view. The S-QoL is a multidimensional instrument. Generation of the items was based on three series of semi-directive interviews with patients' various types (hospitalized, ambulatory, acute phase, stabilized...). Synthesis of the interviews permitted the elaboration of a pre-questionnaire of 97 items.

Setting: A first version of the questionnaire (V0) was used in a sub-group of 141 schizophrenic patients. After a preliminary study of the psychometric properties a first questionnaire (V1) of 53 items was elaborated. A second experimental study was performed in a group of 207 patients. A shorter version (41 items) was developed and a validation study was conducted. Eight dimensions were isolated.

Methods: Nomological validity was studied with clinical parameters (clinical severity, psychotic symptomatology, global functioning) correlated with the S-QoL. The trait validity was estimated by measuring the correlation of the S-QoL with two other instruments: the QoLi and the SF 36. The test-retest reliability was estimated on a subgroup of 53 patients stabilized in a 30-day period.

Results: The coefficients of correlation were from 0.64 to 0.79. The acceptability of the S-QoL was good (missing rate of data lower than 10% for all the scores and the rate of spontaneous refusal between 8 and 12%). The average time of completion was 13.6 +/- 10.8 minutes. Sensitivity to change was studied in a population of 46 patients between day 0 and day 30. The S-QoL was also sensitive to the change. The S-QoL measures the impact of schizophrenia on quality of life of the individuals suffering from the disease.

Conclusion: The S-Qol is a new self-administered questionnaire able to follow the evolution of the disease. S-Qol covers domains that differ from areas tapped in other measures of quality of life. The use of the S-QoL in the assessment of the efficacy of the clinical programme will be evaluated.