Measurement limit of quality-of-life questionnaires in psychiatric settings.

PURPOSE

The extent to which psychiatric patients with a broad spectrum of disability can validly self-report on their quality of life (QOL) remains unknown. Therefore, the aim of this study was to clarify the measurement limit of a QOL questionnaire in psychiatric settings.

METHODS

We examined this issue by assessing data quality, reliability, and validity of the MOS 36-Item Short-Form Health Survey (SF-36) in 137 chronically mentally ill inpatients. We also attempted to identify the impact of cognitive impairment on the validity of the SF-36 and ascertain the points throughout the continuum of cognitive functioning at which self-reported data become compromised.

RESULTS

Cognitive functioning was a major determinant of the data quality, and the psychometric properties of this instrument were marginally acceptable only in patients with Mini-Mental State Examination scores of 28 or higher.

CONCLUSIONS

Measuring QOL reliably and validly through self-report may be possible in psychiatric patients with only very slight cognitive impairment. Therefore, interviewer-administered instruments that measure QOL may be preferable to questionnaires in psychiatric settings.