Daily assessments can provide insight into the temporal characteristics of fatigue. They can demonstrate consistency or reveal variability, as when fatigue changes with the underlying medical condition, improves with therapy, or worsens as a medication side effect. We adapted a fatigue measure from the Patient-Reported Outcomes Measurement Information System (PROMIS(®)) for daily assessment and examined its psychometric properties in a month-long prospective study.
Three groups of 100 participants each were drawn from two fatigue-related clinical disorders [osteoarthritis (OA) and premenstrual syndrome/premenstrual dysphoric disorder (PMS/PMDD)], and a general population sample (GP). They completed brief daily web-based fatigue measures at home on 28 consecutive evenings.
Compliance was high for all samples, based on the percent of participants who remained in the study (98 % for GP and OA, 95 % for PMS/PMDD). The new scale performed consistently across the groups, sensitively measuring fatigue with high reliability (>0.90) especially in the average to high fatigue level range. Supporting known-groups validity, fatigue scores were elevated in the clinical groups as compared to the GP. The scale was sensitive to change, with the PMS/PMDD sample showing a linear increase in fatigue prior to menses onset, and a sharp drop off afterward.
The scale was psychometrically sound across diverse clinical and general population samples, though less reliable when assessing lower levels of fatigue.