We also included the cost of equity

We also included the cost of equity capital, cost of debt capital (interest expense over the sum of long-term debt and current liabilities), and overall cost of capital to find the matching control firms that have similar financing cost prior RFID adoption. Finally, we included industry (four-digit SIC) and year fixed effects to match RFID-adopting firms with control firms in the same industry and year. This made sure that the environment of control firms is similar to that of sample firms. Due to a lack of available data, we are unable to control all factors. Those unknown factors not included in the regression are normally held by all firms and are treated as the error term in the logistic regression model [89]. In sum, the propensity score, taken as equal to the probability of RFID adoption, was estimated by the following logistic model: