Poor agreement found between self-report and a public registry on duration of sickness absence

Objective To investigate the agreement between self-report and a public registry regarding the occurrence and duration of sickness absence (SA) in patients with sciatica. Study Design and Setting Observational 2-year longitudinal study including 227 patients. Self-report SA data were obtained by postal questionnaires covering recall periods of 3, 6, and 12 months and compared with data from the Norwegian National Sickness Benefit Register. Results The percent agreement on the occurrence of SA between self-report and registry was above 85% for all three recall periods. The patients overestimated the duration of their SA by 2.4 (95% confidence interval, 1.1–3.7) weeks for the 3-month recall period. The 95% limits of agreement were generally wide, varying from −12.5 to 17.3 weeks for the 3-month recall period to −38.8 to 37.2 weeks for the 12-month period. For the 3-, 6-, and 12-month recall periods, 48.1%, 29.8%, and 27.3% of the patients reported an SA duration that differed by ≤1 week from that recorded in the registry. Conclusion Mainly because of low precision, the agreement on the duration of SA was poor for all three recall periods. The agreement between self-report and registry regarding the occurrence of SA was good.