II. Methodology and Data
The theoretical framework of study is built from the theory of efficient markets. In order the to analyze the performance of the commercial banks of Thailand, relevant benchmarks have been chosen, and the purpose of this research is to explore whether the commercial banks are able to outperform from SET banking sector index. This study examines the risk-adjusted return of the commercial based on estimation of the Capital Asset banks using Jensen's alpha Pricing Model(CAPM), and there are several reasons of that. Firstly, the interpretation of Jensen's alpha is easier, as it shows the percentage in excess of risk premium that a share has earned compared to its benchmark Secondly, Jensen's alpha is calculated using regression analysis, meaning that it can directly be seen from the output, depending on the statistical results. Therefore, Jensen's alpha(1968) suggests a different concept of risk. Jensen is concerned only with systematic risk(Beta) for scaling the returns of the share. Based on the above-mentioned, Jensen's alpha will be used for the commercial banks'performance in this study. This measure of abnormal return can be defined as: