Table 1.

Characteristics of the Swedish, Danish and Norwegian data collections used to derive the analytical RA treatment cohorts

Country	Sweden			Denmark		Norway
Source cohort	EIRA	SRQ	SRQ biobank	DANBIO	DRB*	NOR-DMARD	ULRABIT	ARCTIC	NOR-VEAC
Years of operation	1996 and onwards	1995 and onwards	2012 and onwards	2000 and onwards	2015 and onwards	2000 and onwards	2010–2013	2010–2015	2010–2016
Early or Established RA	Early	Early and established	Early and established	Early and established	Early and established	Early and established	Established	Early	Early
Coverage	Central and southern parts of Sweden	Nationwide	Some 14 participating centres across the country	Nationwide	10–12 participating centres across the country	Currently 4 (previously 6) geographically spread hospitals in Norway	From single site	13 Norwegian Rheumatology clinics	Seven RA clinics in central and southern Norway
RA inclusion criteria	Newly diagnosed RA diagnosed by a rheumatologist (EULAR/ACR 2010 or ACR 1987)	Clinical diagnosis of RA by a rheumatologist (EULAR/ACR 2010/ACR 1987)	Inclusion in SRQ, plus: early RA, or starting or having stared a b/tsDMARD during the last 2 years.	Clinical diagnosis of RA by a rheumatologist (EULAR/ACR 2010/ACR 1987)	Inclusion in DANBIO	Clinical diagnosis of RA by a rheumatologist (EULAR/ACR 2010 or ACR 1987)	Clinical diagnosis of RA by a rheumatologist (ACR 1987)	Clinical diagnosis of RA by a rheumatologist (EULAR/ACR 2010 or ACR 1987)	Clinical diagnosis of RA by a rheumatologist (EULAR/ACR 2010 or ACR 1987)
Study design	Research project. Incident case–control study with RA as incident cases and population-based controls	Nationwide prospective clinically integrated quality of care register with data entry by the rheumatologist and the patient	Research project. Cohort study.	Nationwide prospective clinically integrated quality of care register with data entry by the rheumatologist and the patient	Research project affiliated to DANBIO	Longitudinal observational study	Longitudinal observational study	Randomised controlled trial	Longitudinal observational study
Data capture	Questionnaires and blood samples	Data entered by the rheumatologist and the patient	One-time blood sample	Data entered by the rheumatologist and the patient	Blood sample (one or several per patient)	Data entered by the rheumatologist and the patient, 1–2 blood samples on subset of patients	Data entered by the rheumatologist and the patient, multiple blood samples per patient	Data entered by the rheumatologist and the patient, multiple blood samples per patient	Data entered by the rheumatologist and the patient, multiple blood samples per patient

*DRB is a subcohort of the DANBIO cohort.

ACR, American Congress of Rheumatology; ARCTIC, Aiming for Remission in rheumatoid arthritis: a randomised trial examining the benefit of ultrasound in a Clinical TIght Control regimen; DANBIO, Danish Registry for Biologic Therapies in Rheumatology; DMARD, disease-modifying antirheumatic drug; DRB, Danish Rheumatologic Biobank; EIRA, Epidemiological Investigation of RA; EULAR, European Alliance of Associations for Rheumatology; NOR-DMARD, The Norwegian Antirheumatic Drug Register; NOR-VEAC, Norwegian Very Early Arthritic Clinic; RA, rheumatoid arthritis; SRQ, Swedish Rheumatology Quality register; ULRABIT, ULtrasound in Rheumatoid Arthritis patients starting BIologic Treatment.