The purpose of this study is to compare the risk of major bleeding event among nonvalvular atrial fibrillation patients treated with warfarin, apixaban, dabigatran and rivaroxaban.

Inclusion Criteria:

• Patients ≥18 years old as of the index date
• At least 1 diagnosis of atrial fibrillation in the 12 months prior to or on index date, identified by any medical claim
• At least one year of baseline period and continuous enrollment for at least 12 months prior to index date Individuals with NVAF who were using oral anticoagulants (i.e., warfarin, dabigatran, rivaroxaban and apixaban) within the study period beginning Jan 1, 2012 through December 31, 2013 or last date of the last data cut available at the time of execution of the study

Exclusion Criteria:

• Patients with evidence of valvular heart disease, thyrotoxicosis, pericarditis, mitral stenosis, Venous thromboembolism(VTE), heart surgery, and endocarditis during the baseline period any time prior to or on index date
• Patients with any evidence of pregnancy at any time during the baseline will be excluded

Patients 18 years of age and older with Non-Valvular Atrial Fibrillation (NVAF) using oral anticoagulants