Statistical analysis
We carried out chi-square analysis in order to compare the biologics and non-biologics groups. We compared the characteristics of the biologics patients and non-biologics patients, adopting the t-test for continuous variables and the chi-square test for categorical variables. The incidence of mortality was reported as the event rate (proportion of events) and incidence density (number of events per 100 person-years). We adopted Cox proportional hazard model to compare the risk of mortality between the two groups. Furthermore, we used the Poisson regression model to compare the annual number of admissions for autoimmune disease between the study groups, treating the log-transformed follow-up year as an offset variable. Finally, the hazard ratio of the patients of the two groups was calculated with survival analysis. We considered a p -value < 0.05 to be statistically significant. All data analysis was conducted using SAS software version 9.4 (SAS Institute, Cary, NC).
-       Ethics approval and consent to participate
This retrospective database analysis study involving human participants was in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. The Longitudinal Health Insurance Database 2005 provides only de-identified samples, which Ethical approval was waived by the local Ethics Committee.