A study is carried out investigating the risk of suffering a stroke in patients with atrial fibrillation taking the new anti-platelet drug ticagrelor, compared with standard treatment with warfarin. The patients were followed over a 2-year time period. 300 patients took ticagrelor and 500 patients took warfarin. In the ticagrelor group 30 patients suffered a stroke and in the warfarin group 20 patients suffered a stroke over the 2-year period.
What is the relative risk of a stroke? Select ONE answer only.