How Should Thyroid-Related Quality of Life Be Assessed? Recalled Patient-Reported Outcomes Compared to Here-and-Now Measures.

Background: The impact of thyroid disease on quality of life is an important disease aspect that is best investigated by patient-reported outcomes. Recent patient-reported outcomes research has raised concern about the validity of traditional retrospective questionnaires. Therefore, ecological momentary assessments of patients' subjective well-being have been introduced to avoid recall bias and improve contextual validity. Despite theoretical advantages, the measurement properties remain unsubstantiated. This study examines the relationship between the retrospective thyroid-related quality of life patient-reported outcome measure (ThyPRO) and a momentary (here-and-now) version of ThyPRO.

Methods: Eighty-three newly diagnosed hyperthyroid patients expected to undergo treatment completed questions on their thyroid-related quality of life. Head-to-head comparison was performed between 12 momentary items from four multi-item ThyPRO scales administered three times daily via a smartphone application during 28 days and the original retrospective ThyPRO on day 28. The measurement difference between recalled and momentary ratings was quantified for all four scales. Furthermore, correlations between the measures were investigated, and their agreement was explored using Bland-Altman plots. Finally, the study examined whether retrospective ratings were influenced by two forms of recall bias (the peak effect and the end effect).

Results: Retrospective and mean momentary ThyPRO ratings were highly correlated (Pearson's correlations: 0.74-0.88). However, retrospective ratings provided significantly higher scores (i.e., worse quality of life) on all scales. Bland-Altman plots showed a skewed distribution, indicating low levels of agreement. Results supported a peak effect for retrospective ratings on tiredness but not for the remaining scales. Further, results supported end effects for retrospective ratings of emotional susceptibility and anxiety.

Conclusions: Retrospective and mean momentary ThyPRO ratings correlated strongly, but retrospective ratings were higher, indicating more disease impact. The differences were of magnitudes normally deemed clinically relevant. Limited evidence supported peak and end effect bias for retrospective assessments. The two measurement modalities did not appear congruent and thus cannot be used interchangeably. When designing clinical studies, whether to use a momentary or retrospective measurement method may depend on the aim of measurement. Further prospective analyses are needed to compare any beneficial effects, for example in terms of higher precision or sensitivity to clinical change, of momentary assessments.