“…IRs in 2018 varied from 17 to 19 and 8 to 9 per 100 000 PY for seropositive and seronegative RA, respectively, depending on the outcome definition of seropositivity applied. Both estimates were lower than reported in other Western countries except in Greece, though heterogenicity between the studies existed (18,106,109,110). Besides the heterogeneity in methodological approaches, these differences might be due to the suspected underestimation of IRs in 2017 and 2018 in Study II caused by delayed and suboptimal registration in the DNPR after the introduction of a new healthcare information technology system in two of the Danish regions (Appendix B) (1).…”