Syncope is a common Emergency Department (ED) presentation. An important proportion of syncope patients are at risk of developing serious adverse events (SAEs), such as deaths or arrhythmias following ED disposition. Currently, no clinically-useful decision tool exists to reliably identify high-risk patients. This study derived a clinical decision tool to identify syncope patients at risk of developing SAEs after ED disposition. This study also examined key methodological considerations involved in deriving decision tools by comparing two different methodological approaches: a traditional and modern approach. The traditional approach led to an eight-variable decision tool that allowed simple clinical interpretation and use. The modern approach, which aims to avoid data-driven methodology and statistical overfitting, was used to derive a ten-variable decision tool. Both decision tools displayed acceptable and comparable performance in internal validation studies (c-statistic 0.87, 95% confidence interval 0.84-0.89). A future external validation study is required to comprehensively compare the methods.