Shorter recall period for the thyroid-related patient-reported outcome measure ThyPRO did not change the accuracy as evaluated by repeated momentary measurements

Background: The thyroid-related patient-reported outcome measure ThyPRO has become the gold standard for measuring thyroid-related quality of life and uses a 4-week recall period. The impact of the length of recall is unresolved. To minimize recall bias, the US Food and Drug Administration has argued in favor of short recall periods or measures describing current states. We investigated whether a 1-week recall version of ThyPRO was less prone to recall bias than the original ThyPRO, using averaged momentary ThyPRO measurements as the hypothesized true mean of patients' symptoms. Methods: Patients newly diagnosed with thyrotoxicosis were included (N = 122). During a 28-day study period, participants answered momentary questions three times daily via a smartphone, weekly retrospective surveys with a 1-week recall period, and the original survey with a 4-week recall period on day 28. Twelve ThyPRO items from four multi-item scales were used. Mean momentary ratings for each scale were compared with recall ratings of 1- and 4-week periods, respectively. Results: The mean momentary ratings were highly correlated with retrospective ratings and remained rather constant when altering the reporting period from four weeks to one week. We found consistently lower scores (i.e., better thyroid-related quality of life) on momentary ratings compared with retrospective ratings. The mean differences between momentary ratings and retrospective ratings were similar for both recall periods. The original 4-week ThyPRO accurately summarized the mean of all 1-week ThyPROs. Conclusions: Shortening the recall period of ThyPRO from four weeks to one week was not associated with less recall bias within this subset of items. Nor did 1-week recall seem to compromise the accuracy of ThyPRO. Thus, either version of ThyPRO can be used in future studies.