Recall of health-related quality of life: how does memory affect the SF-6D in patients with psoriasis or multiple sclerosis? A prospective observational study in Germany.

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&#95;RECALL&#95;16&#95;003837.
Competing Interests: Competing interests: None declared.
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