Purpose: This study examined the impact of different reporting period lengths on the accuracy of items measuring interference due to pain and fatigue with work, walking, and relations with others.
Methods: Six items from well-established instruments (Brief Pain Inventory, Brief Fatigue Inventory, SF-36) were investigated in a prospective study of 117 patients with chronic rheumatological illness. Daily ratings were compared with recall ratings of 1, 3, 7, and 28-day reporting periods.
Results: The level of recall ratings (RRs) for reporting periods of 3 days or more were significantly higher than the level of aggregated end-of-day (EOD) ratings. Correspondence between aggregated EOD and RRs was good (r ≥ .80) regardless of the length of the reporting period. Ratings of interference for a single day were highly correlated with aggregated EOD for up to 14 days prior to the single rating (r ≥ .76).
Conclusions: Recall ratings with reporting periods of up to a month yield good correspondence with aggregated daily ratings, although the absolute level of the rating will be inflated for recall periods of 3 days or longer.