Assessing health utilities in schizophrenia. A feasibility study

Utility, a concept derived from economics, is the desirability or preference that individuals exhibit for a certain health state. Utility measurement could be viewed as an alternative means of appraising the quality of life of individuals affected by a chronic illness such as schizophrenia. Traditional techniques of utility measurement involve 2 steps: (i) identifying the different health states experienced by individuals during the course of an illness; and (ii) assigning them numerical values known as utilities.

The study examined the feasibility issues and psychometric aspects of obtaining accurate health state descriptions and their utilities from symptomatically stable patients with schizophrenia.

The study used a cross-sectional, case-controlled design, with a study group consisting of 120 clinically stabilised patients with schizophrenia and a control group of 32 treated and recovered patients with major depression. Patients were asked to provide detailed descriptions of 3 distinct health states associated with their illness: current state, worst state experienced since the onset of illness and a perfect state desired in the future. Further, patients were asked to assign utilities to these health states with the aid of a purpose-built evaluation protocol comprising Magnitude Estimation (ME), Rating Scale (RS), Standard Gamble (SG), Time Trade-Off (TTO) and Willingness-to-Pay (WTP) techniques. The battery was repeated after a 1-week interval. Independent raters assessed symptom severity, insight and quality of life, and nurse-clinicians involved in their care were asked to provide the utility ratings of their clients' mental health state. Patients' opinions about the acceptability of utility measurement techniques, and the respondent burden were also ascertained.

Compared with control patients with treated depression, patients with schizophrenia were able to distinguish and describe the specified health states with an equal degree of ease and accuracy. RS, TTO and WTP techniques emerged as the favoured methods of utility evaluation. The test-retest reliability of utility ratings (r = 0.87 to 0.97; p < 0.001) was high, and concurrent validity with the quality of life measures was acceptable. Reliability and validity of patients' appraisals were unaffected by symptoms severity and insight. The accuracy of nurse-clinicians' appraisals were dependent on their close familiarity with the patients and their illness.

Clinically stabilised patients with schizophrenia can provide accurate health state descriptions and assign them utilities with a fair degree of reliability and validity. Utility evaluations based on patients' self-appraisals can be seen as potential tools in outcome studies and clinical trials involving patients with schizophrenia, but the methodology requires further refinement to accommodate the limitations imposed by the patients' disturbed mental status.