Detection of arbitrarily-shaped clusters using a neighbor-expanding approach: a case study on murine typhus in south Texas.

Zhijun Yao,Junmei Tang,F Benjamin Zhan

doi:10.1186/1476-072x-10-23

Zhijun Yao, Junmei Tang + Show 1 more

Open Access

https://doi.org/10.1186/1476-072x-10-23

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Abstract

BackgroundKulldorff's spatial scan statistic has been one of the most widely used statistical methods for automatic detection of clusters in spatial data. One limitation of this method lies in the fact that it has to rely on scan windows with predefined shapes in the search process, and therefore it cannot detect cluster with arbitrary shapes. We employ a new neighbor-expanding approach and introduce two new algorithms to detect cluster with arbitrary shapes in spatial data. These two algorithms are called the maximum-likelihood-first (MLF) algorithm and non-greedy growth (NGG) algorithm. We then compare the performance of these two new algorithms with the spatial scan statistic (SaTScan), Tango's flexibly shaped spatial scan statistic (FlexScan), and Duczmal's simulated annealing (SA) method using two datasets. Furthermore, we utilize the methods to examine clusters of murine typhus cases in South Texas from 1996 to 2006.ResultWhen compared with the SaTScan and FlexScan method, the two new algorithms were more flexible and sensitive in detecting the clusters with arbitrary shapes in the test datasets. Clusters detected by the MLF algorithm are statistically more significant than those detected by the NGG algorithm. However, the NGG algorithm appears to be more stable when there are no extreme cluster patterns in the data. For the murine typhus data in South Texas, a large portion of the detected clusters were located in coastal counties where environmental conditions and socioeconomic status of some population groups were at a disadvantage when compared with those in other counties with no clusters of murine typhus cases.ConclusionThe two new algorithms are effective in detecting the location and boundary of spatial clusters with arbitrary shapes. Additional research is needed to better understand the etiology of the concentration of murine typhus cases in some counties in south Texas.

Highlights

In recent years, there has been a significant increase in public concern about environmental hazards and disease events [1]
The two new algorithms are effective in detecting the location and boundary of spatial clusters with arbitrary shapes
Performance Test Using Simulated Data and Benchmark Data We evaluated the performance of the two new algorithms and compared them with the simulated annealing (SA) strategy method, flexible-shape scan statistic (FlexScan), and spatial scan statistic (SaTScan) before we applied the algorithms to the south Texas data

Summary

Introduction

There has been a significant increase in public concern about environmental hazards and disease events [1]. Rather than specifying the size of a potential cluster a priori, this method uses a scan window of varying sizes, corresponding to varying population and varying number of incidents. This method has been applied to many research fields. The spatial scan statistic and other similar approaches suffer from some restrictions in practice [14,15] This method can be adopted to include any shape for scan windows [7], it still has limitation in practice due to the predefined geometrical shapes of scan windows [15] which leave a large number of candidate clusters out of the test. We employ a new neighbor-expanding approach and introduce two new algorithms to detect cluster with arbitrary shapes in spatial data. We utilize the methods to examine clusters of murine typhus cases in South Texas from 1996 to 2006

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