Major guidelines have used the above fixed annual stroke risk as a guideline of starting anticoagulant treatment; where the ischemic stroke risk of more than 1% to 2% should be an indication to start an anticoagulant therapy. However, actual risk of getting stroke varies according to sampling method and geographical regions, as well as use of appropriate study analysis methodology. A meta-analysis of various studies in 2015 shown that annual stroke risk is less than 1% in 13 of the 17 studies for CHA2DS2-VASc score of 1, 6 out of 15 studies reported risk of 1 to 2% and 5 out of 15 studies reported risk of more than 2% for CHA2DS2-VASc score of 2. Nevertheless, stroke rates vary by study setting (hospital vs community), population (trial vs general), ethnicity, etc. Some studies included in the metaanalysis include females with score 1 by virtue of gender (who are low risk), into the aggregate rates; others included do not account for followup anticoagulation use (thus lowering rates) and were analysed by excluding all patients ever started on anticoagulants ('conditioning on the future' error). The CHA2DS2-VASc Score has shown increasing popularity over time while the CHADS2 has shown decreasing popularity, which could "partly be related to introduction of guidelines recommending the use of the CHA2DS2-VASc score for stroke risk stratification". The CHA2DS2-VASc score has been used in the 2012 European Society of Cardiology guidelines for the management of atrial fibrillation. The 2014 American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society guidelines also recommend use of the CHA2DS2-VASc score. The European Society of Cardiology (ESC), and National Institute for Health and Care Excellence (NICE) guidelines recommend that if the patient has a CHA2DS2-VASc score of 2 and above, oral anticoagulation therapy (OAC) with a Vitamin K Antagonist (VKA, e.g. warfarin with target INR of 2-3) or one of the direct oral anticoagulant drugs (DOACs, e.g. dabigatran, rivaroxaban, edoxaban, or apixaban) is recommended. If the patient is 'low risk' using the CHA2DS2-VASc score (that is, 0 in males or 1 in females), no anticoagulant therapy is recommended.