From Table 1, the results show that in all but two years(2009 and 2011) over the seven-year period examined, the annual average alpha values were positive, indicating the above average performance in comparison to the SET banking sector index of 11 commercial banks, while positive, is not statistically significant. Therefore, an inconsistent decrease in average standard deviations of alpha values would suggest an unstable banking industry as measured by return performance. The results support the rejection of the alternative hypothesis and the acceptance of the null hypothesis at the 5% and 10% significance levels over the study periods. This suggests that the commercial bank performance levels are not different to the SET banking sector index.
In the case of each commercial bank, the results show that there is a significant statistical difference existing between average alpha value and zero at the 5% and at the 10% significance level for Kasikornbank Public Co Ltd in 2010 and 2012, respectively. Therefore, Siam Commercial Bank PLC. shows that the performance levels are outperform the SET banking sector index in 2011 at the 10% significance level. That claim that domestic commercial banks, at least Kasikornbank Public Co Ltd and Siam Commercial Bank PLC. are efficiently priced in exploitable ways is a myth. Thus, the findings that reveal a high number of domestic commercial banks with insignificant positive alpha values support the efficient market hypothesis, which suggests there is no potential to gain abnormal returns with publicly available information.
Table 2 reports the alpha values and standard deviations of alpha values for each commercial bank over the seven-year period analyzed. Accordingly, the difference between the average alpha values and zero can be measured to determine if the difference is significant using t- statistic.
From Table 2, the results support the rejection of the null hypothesis and the acceptance of the null alternative hypothesis at the 5% significance levels over the study period The results show that the commercial bank performance levels are different to the SET banking sector index. The performance measures reveal that domestic commercial banks achieved superior performance levels to banking market over the full period. It can be argued that the the banking markets are somehow efficient even though they do take a longer period of time to adjust themselves in accordance with relevant information. This corresponds with the efficient market hypothesis(Kuble, Waltber, & Wurtzebach, 1986). The results in Table 1 support this claim. That is, the years 2012 through 2014 reflect a period of low average alpha values for all commercial banks. This trend, if continued, will in theory result in alpha values equal to zero.