Group-sequential analysis may allow for early trial termination: illustration by an intra-observer repeatability study

Background: Group-sequential testing is widely used in pivotal therapeutic, but rarely in diagnostic research, although it may save studies, time, and costs. The purpose of this paper was to demonstrate a group-sequential analysis strategy in an intra-observer study on quantitative FDG-PET/CT measurements, illuminating the possibility of early trial termination which implicates significant potential time and resource savings.
Methods: Primary lesion maximum standardised uptake value (SUVmax) was determined twice from preoperative FDG-PET/CTs in 45 ovarian cancer patients. Differences in SUVmax were assumed to be normally distributed, and sequential one-sided hypothesis tests on the population standard deviation of the differences against a hypothesised value of 1.5 were performed, employing an alpha spending function. The fixed-sample analysis (N = 45) was compared
with the group-sequential analysis strategies comprising one (at N = 23), two (at
N = 15, 30), or three interim analyses (at N = 11, 23, 34), respectively, which were defined post hoc.
Results: When performing interim analyses with one third and two thirds of patients, sufficient agreement could be concluded after the first interim analysis and the final analysis. Other partitions did not suggest early stopping after
adjustment for multiple testing due to one influential outlier and our small sample size.
Conclusions: Group-sequential testing may enable early stopping of a trial, allowing for potential time and resource savings. The testing strategy must, though, be defined at the planning stage, and sample sizes must be reasonably
large at interim analysis to ensure robustness against single outliers. Group-sequential testing may have a place in accuracy and agreement studies.