The objective of this work was to develop a psychometrically sound questionnaire for measuring the on-the-job impact of chronic health problems and/or treatment ("work limitations").
Three pilot studies (focus groups, cognitive interviews, and an alternate forms test) generated candidate items, dimensions, and response scales. Two field trials tested the psychometric performance of the questionnaire (studies 1 and 2). To test recall error, study 1 subjects were randomly assigned to 2 different questionnaire groups, a questionnaire with a 4-week reporting period completed once or a 2-week version completed twice. Responses were compared with data from concurrent work limitation diaries (the gold standard). To test construct validity, we compared questionnaire scores of patients with those of healthy job-matched control subjects. Study 2 was a cross-sectional mail survey testing scale reliability and construct validity.
The study subjects were employed individuals (18-64 years of age) from several chronic condition groups (study 1, n = 48; study 2, n = 121) and, in study 1, 17 healthy matched control subjects.
Study 1 included the assigned questionnaires and weekly diaries. Study 2 included the new questionnaire, SF-36, and work productivity loss items.
In study 1, questionnaire responses were consistent with diary data but were most highly correlated with the most recent week. Patients had significantly higher (worse) limitation scores than control subjects. In study 2, 4 scales from a 25-item questionnaire achieved Cronbach alphas of > or = 0.90 and correlated with health status and self-reported work productivity in the hypothesized manner (P < or = 0.05).
With 25 items, 4 dimensions (limitations handling time, physical, mental-interpersonal, and output demands), and a 2-week reporting period, the Work Limitations Questionnaire demonstrated high reliability and validity.