Sample size and power calculation. The sample sizes were calculated based on the frequency of psychological distress, which is the most interesting potential risk factor for ischemic stroke in the young. According to a previous report comparing psychological distress in ischemic stroke patients and healthy controls,8 the frequency of stress was 50.3% in the ischemic stroke patients and 38.6% in the healthy controls; a difference of 11.7%. To detect such a difference with a power of 90% and alpha of 0.05 with a drop-out rate of 20%, a sample size of at least 470 patients and 470 controls will be needed (PASS 13).