Table 1

Variables used to assess factors associated with switching (present on the first day of the follow-up period unless otherwise stated)

Factor	Detailed information on coding	Codelist (where applicable)
Age group	<65, 65–74 and 75+
Indices of Multiple Deprivation (IMD)	Deciles based on residential postcode	Supplied by TPP.
Sustainability and transformation partnership (STP) membership	STP of current registered practice – modelled as a random effect	STP are NHS administrative regions made up of one or more CCGs. Linkage to national STPs carried out by TPP.
Care/nursing home residence status	Yes/no	Classification supplied by TPP based on patient’s residential address at 1 February 2020 linked to CQC care home register.
Diagnosis of AF	Yes/no; any time prior to follow-up period	https://codelists.opensafely.org/codelist/opensafely/atrial-fibrillation /2020-07-09/
Renal function	Latest estimated Glomerular Filtration Rate (eGFR function) (<30, 30–59 and ≥60) in the 12 months to the end of the baseline period (or ‘no evidence’ for those with no creatinine recorded in this period).	eGFR calculated from creatinine records. Creatinine clearance is recommended renal function assessment for tailoring DOAC doses for individual people. Automated calculation of Creatinine Clearance (CrCl) is not yet available in OpenSAFELY, and eGFR is used as pragmatic alternative.
Recent renal function test	Yes/no; within last 4 months and up to the end of the study period (this conservatively allows tests slightly outside of the recommended 3-month period, and any time during the switching period).	Creatinine test or: ‘451’. Renal function test. ‘XacUK’ eGFR using creatinine (calculated using Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI) per 1.73 square metres.
Number of INR tests	0, 1–3, 4–6 or 7+ tests during the baseline period	https://codelists.opensafely.org/codelist/opensafely/international-normalised-ratio -inr/2020-10-22
Length of time on warfarin*	<2 years (since 16 March 2018). 2–≤6 years (since June 2014, date of latest National Institute of Health and Care Excellence (NICE) AF guidance).22 6–<8 years (since March 2012, date of first NICE Technology Appraisal for a DOAC for AF).23 ≥8 years.	https://codelists.opensafely.org/codelist/opensafely/warfarin/2020-10-05/
Previously prescribed DOACs*	Yes/no; any time prior to the baseline period.	https://codelists.opensafely.org/codelist/opensafely/direct-acting-oral-anticoagulants -doac/2020-10-05/
Explicitly recorded contraindicaton to DOAC	Yes/no; any time prior to the follow-up period.	https://codelists.opensafely.org/codelist/opensafely/explicit-contraindication-to-doacs-direct-acting-anticoagulants/2020-10-19/

*The earliest actual date of an event may be missing due to incomplete patient records (eg, lost in transfer between practices), but the earliest recorded date can be used as an approximation.
AF, atrial fibrillation; CCGs, Clinical Commissioning Groups; DOAC, direct-acting oral anticoagulant; INR, international normalised ratio; NHS, National Health Service.