Sample size A difference between groups equivalent to one standard deviation was perceived to be of clinical importance. With 30 subjects per group, this study had a 97% power to detect a difference equal to one standard deviation with a two-sided p-value of 0.05. A minimum of 16 subjects per subgroup was required for this study to have an 80% power to detect a difference equal to one standard deviation with a two-sided p-value of 0.05.