Does accounting for seizure frequency variability increase clinical trial power?

•The expected range of seizure frequencies can be predicted several months in advance.•Using these predictions, a new trial analysis method ZV was introduced.•Compared to 50%-responder rates (RR50), ZV has higher statistical power to distinguish the placebo arm from the therapeutic arm.•Use of ZV in trial analysis may allow for design of epilepsy trials with decreased sample size and cost. Seizure frequency variability is associated with placebo responses in randomized controlled trials (RCT). Increased variability can result in drug misclassification and, hence, decreased statistical power. We investigated a new method that directly incorporated variability into RCT analysis, ZV. Two models were assessed: the traditional 50%-responder rate (RR50), and the variability-corrected score, ZV. Each predicted seizure frequency upper and lower limits using prior seizures. Accuracy was defined as percentage of time-intervals when the observed seizure frequencies were within the predicted limits. First, we tested the ZV method on three datasets (SeizureTracker: n=3016, Human Epilepsy Project: n=107, and NeuroVista: n=15). An additional independent SeizureTracker validation dataset was used to generate a set of 200 simulated trials each for 5 different sample sizes (total N=100 to 500 by 100), assuming 20% dropout and 30% drug efficacy. “Power” was determined as the percentage of trials successfully distinguishing placebo from drug (p90% power at N=100 per arm while RR50 required N=200 per arm. ZV may increase the statistical power of an RCT relative to the traditional RR50.