Common use of Statistical Power Clause in Contracts

Statistical Power. The study had 51% statistical power to detect an absolute difference of 30 percentage points between the PVI and IC groups’ rates of virologic suppression at a 5% significance level for a two-sided test. Comparing the IC and PC arms, the study had 67% power to detect the same difference. We used logistic regression to estimate the unadjusted and adjusted impact of the IC treatment relative to the PVI arm and relative to the PC arm. The predictor variables included treatment arm indicators and the stratifying variable. Our hypothesis tests were constructed relying on the asymptotic normality of the maximum likelihood estimator, but we obtained similar results when we conducted permutation tests. All statistical procedures were implemented using Stata 13 (StataCorp, College Station, TX, USA). Supplementary analyses indicate that the three arms had similar demographic and clinical characteristics at baseline, although individuals in the PC arm were older (median age 48.93 years) than individuals in the IC arm (median 40.10) and PVI arm (median 42.88). Individuals in the IC arm had higher pVL values leading up to the enrollment visit relative to individuals in the other arms. The PC arm had a higher rate of missing pVL measurements at the fifth study visit compared to the other arms. In the IC arm, 48% of participants had at least one suppressed viral load measurement across the three visits prior to the enrollment visit. The percentage was 43% in the PVI arm and 36% in the PC arm. Thus, many individuals in the study had experienced some previous success in achieving viral suppression, although some individuals in the study had faced much more difficulty achieving success in the past.