Assessing the consistency and validity of self-reported year of diagnosis among participants in a longitudinal study of people with multiple sclerosis

Background: Self-reported outcomes are important for epidemiological research but are vulnerable to bias.

Objective: In this study, we evaluated: 1) the consistency and validity of self-reported year of diagnosis among people living with MS, 2) factors associated with participant inconsistency, and 3) the impact of observed inconsistency on the calculation of the Multiple Sclerosis Severity Score (MSSS).

Methods: Using data collected by the Australian MS Longitudinal Study, we evaluated the consistency of self-reported year of diagnosis using correlation, mean differences, and percentage agreement. We examined the impact of participant characteristics using Cragg hurdle models, and determined the effect of the observed inconsistency on MSSS using simulations compared with paired t-tests.

Results: Of the 2,445 participants, 80.3% were within 1 year of their baseline year of diagnosis in all subsequent responses (range of 2-10 responses). Participant inconsistency was positively associated with age at first response and the number of years elapsed between the first and final response. However, the effect sizes of these associations were small. Finally, the observed inconsistency did not affect the calculation of MSSS (mean difference smaller than 0.01; p>0.90 for all comparisons).

Conclusion: This data provides support for the use of patient-reported year of diagnosis, as people with MS were consistent in reporting their year of diagnosis and the impact of any inconsistency on clinical outcomes, such as the MSSS, was negligible.