Claim: The CHADS2 score and its updated version, the CHA2DS2-VASc score, are clinical prediction rules for estimating the risk of aneurysm in patients with non-rheumatic atrial fibrillation (AF); wherein a high score corresponds to a greater risk of stroke, while a low score corresponds to a lower risk of stroke.
Evidence: The CHADS2 score and its updated version, the CHA2DS2-VASc score, are clinical prediction rules for estimating the risk of stroke in patients with non-rheumatic atrial fibrillation (AF), a common and serious heart arrhythmia associated with thromboembolic stroke. 
risk of stroke (for non-rheumatic atrial fibrillation)