Evaluation of hotspot cluster detection using spatial scan statistic based on exact counting

In this paper, we propose a novel approach to the detection of spatial clusters based on linkage information of a map dataset. Spatial scan statistic has been widely used for detecting a hotspot cluster (or a coldspot cluster) in various fields, such as astronomy, biosurveillance, natural disasters, and forestry. This approach is based on the idea of finding a connected regional subset that maximizes likelihood in the whole study area. To detect a hotspot cluster, which aggregates high-risk regions so as to be maximum likelihood, we only just search such a cluster from all patterns of connected regional subsets. However, except when there are extremely few regions of the study area, since the total number of connected regional patterns usually becomes enormous, we cannot investigate all of them. This means that we have not been able to know whether a detected hotspot which is obtained under certain rules, such as using the previous studies, has the truly maximum likelihood within a given study area. A zero-suppressed binary decision diagram (ZDD), one approach to frequent item set mining, enables us to extract all of the potential cluster regions at a realistic computational load. In this study, we propose a hotspot detection method using ZDD-based enumeration, and apply it to sudden infant death syndrome in North Carolina. This completely new method enables us to detect a true hotspot cluster that has the truly maximum likelihood. To evaluate our proposed method, we compare the properties of that with existing methods such as flexible scan and echelon scan, and discuss their suitability for different purposes of detecting hotspot.