Utilities of the P-value Distribution Associated with Effect Size in Clinical Trials

The P‐value, which is widely used for assessing statistical evidence in randomized comparative clinical trials, is a function of the observed effect size of the experimental treatment relative to the control treatment. The relationship of the P‐value with the observed effect size at study completion and the effect size anticipated at the design stage has potential usefulness in providing guidance for planning and interpretation of a clinical trial. The post‐trial power associated with a statistically significant P‐value from a completed study is also a random variable and its use may assist in planning a follow‐up trial to confirm the statistically significant findings in an initial study. A measure of robustness is explored to quantify the degree of sensitivity of the observed P‐value to potential bias that may be contained in the observed effect size.