An event study requires defining the event period. We followed procedures from prior studies to define the event period [e.g., 72, 73]. The year of formal RFID adoption when a firm successfully applied full-scale RFID was defined as year t. Given that full-scale integration of RFID into the supply chain system requires approximately one year1 of implementation [80, 81], we used t - 1 as the initiating time of RFID implementation and year t - 2 as the base year that is free from the impact of RFID adoption to match the control firms. The definition is aligned with a previous research by Hendricks et al. [81], suggesting approximately one year for implementing a typical SCM system. Since the payback period for RFID projects is between two and three years [43, 82], we detected the impact of RFID on the cost of equity capital up to three years after the RFID adoption (i.e., t + 1, t + 2, and t + 3). Overall, we studied the cost of equity capital for the period starting from two years before RFID adoption and three years after RFID adoption (i.e., from t - 2 to t + 3). We estimated abnormal performance as the sample post-event performance (i.e., actual performance) minus the expected performance. We calculated the expected performance as the sample post-event performance plus the change of performance of the control firm during the same period [15]. The formula for calculating the abnormal performances as follow: