RESUMO
OBJECTIVE: This study aimed to quantify recall bias in the measurement of health-related quality of life (HRQoL), that is, the extent to which recollection is impaired and leads to distorted judgements. DESIGN: Prospective observational study. SETTING AND PARTICIPANTS: One hundred patients with two paradigmatic chronic diseases (50 with multiple sclerosis and 50 with psoriasis) were recruited at two outpatient clinics. METHODS AND OUTCOME MEASURES: Patients completed the online version of the 12-Item Short Form Survey (SF-12) repeatedly for 28 consecutive days: (1) daily, considering the past 24 hours; (2) weekly, considering the past 7 days; and (3) on the last day of data collection, considering the past 4 weeks. SF-12 scores for all three measurement approaches were subsequently converted into preference-based utility indices (Short-Form Six-Dimension). Agreement of the three indices was analysed on group and individual patient levels. RESULTS: The mean age of participants was 40.3 years (±12.0), and 63% were female. The utility index based on daily recall (0.74±0.13) was more positive than indices based on a weekly (0.70±0.13, p<0.001) or a monthly (0.70±0.14, p<0.001) recall. While agreement of measurement approaches was high on group level (intraclass correlation coefficient>0.85), it was lower for the subgroup of patients experiencing high variability of HRQoL over time. Bland-Altman plots revealed considerable differences on individual patient level. CONCLUSIONS: On the group level, retrospective overestimation and underestimation of HRQoL almost cancelled out one another and recall bias was relatively small. Therefore, a 4-week recall period could be appropriate when group-level data are used for research or economic evaluations. In contrast, recall bias can be considerable on the individual patient level and may thus impact decision-making in clinical practice. TRIAL REGISTRATION NUMBER: VfD_RECALL_16_003837.