In clinical trials, some measures of effect of ratio are used to evaluate the treatment effect between pre- and post-observed values of a drug. The most popular measure of effect of ratio is the percent change (PC), but symmetrized percent change (SPC) is sometimes applied in a trial. Some researchers examined the properties of two measures under the assumption of limited distribution for pre- and post-observed values, such as bivariate normal or bivariate log-normal distribution. In this paper, we evaluated the relationship between the variation of skewness of two measure (PC or SPC) and various shapes of pre- and post-observed data’s distribution, and evaluated the relationship between the statistical power and the variation of skewness of the two measures under the simultanious distribution of pre- and post-observed data following the bivariate power normal distribution. Then, we proposed how to apply the two measures in various situations.