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.
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.
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).
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.