The objective of the study is to evaluate the effectiveness and safety of the reduced dose rivaroxaban (15 mg once daily) as compared to warfarin in non-valvular atrial fibrillation (NVAF) patients with renal dysfunction in routine clinical practice. The study has a retrospective design, and will be conducted in the US Truven Health MarketScan Commercial Claims and Medicare Supplemental Databases

Inclusion Criteria:

• have to be adults (≥18 years of age)
• newly-initiated on warfarin or rivaroxaban 15 mg (index event, index drug)
• have at least 365 days of continuous medical and prescription benefits prior to the index event (baseline period)
• have at least two diagnosis codes for NVAF (on outpatient or inpatient claims, at two different days) and
• have at least one diagnosis code (inpatient or outpatient) indicating renal dysfunction in the baseline period

Exclusion Criteria:

• valvular AF (at least one inpatient diagnosis in the baseline period)
• pregnancy (inpatient or outpatient diagnosis in the baseline period)
• transient cause of AF (inpatient or outpatient diagnosis in the baseline period)
• venous thromboembolism (pulmonary embolism or deep vein thrombosis) (one inpatient or outpatient diagnosis 60 days prior to or on the index date) or
• overcame a hip or knee replacement (one inpatient diagnosis or procedure code 60 days prior to or on the index date)
• have a pharmacy claim for an oral anticoagulation (OAC) dispensation (warfarin, apixaban, dabigatran, edoxaban or rivaroxaban) in the baseline period
• receive both warfarin and rivaroxaban 15 mg on the index date
• have an end-stage kidney disease or be on dialysis (one inpatient or outpatient diagnosis or procedure code in the baseline period).

For the main analysis, patients having malignant cancers (inpatient or outpatient diagnosis in the baseline period) will be excluded. A sensitivity analysis, omitting this exclusion criterion, will be performed.

The source population of this study is all the insured individuals included in the US Truven Health MarketScan Commercial Claims and Medicare Supplemental Databases.To be included in the present study, adult patients have to be diagnosed with NVAF, have renal dysfunction and be newly-initiated on warfarin or rivaroxaban 15 mg for stroke prevention.