EFFECT OF RELATIVE RISK AND CLUSTER CONFIGURATION ON THE POWER OF THEONE-DIMENSIONAL SCAN STATISTIC

The scan test for clustering in time is based on the maximum number of events in an interval (window) of width w as the window moves across the entire time frame. Power estimates of the scan statistic are simul ated for a variety of epidemiologically motivated situations. Two clus ter configurations are used: a rectangular pulse, and a triangular pul se designed to emulate environmental contamination. For a rectangular pulse, the relative risk R of disease in the cluster region is R-fold as high as it is for the background region. The power is strongly infl uenced by the sample size, the relative risk, and the width or duratio n of the cluster region, whereas the effect of the cluster configurati on is small. Using a 5 per cent significance level, a relative risk of 4, a standardized cluster duration of 0.10, a relative window width o f 1.5, and a (non-random) sample size of 50, the simulated power is ap proximately 80 per cent, indicating that the minimum sample size in th e cluster region for adequate power is in the 12-32 range for values o f the parameters used in this study.