Hu Yi, Bergquist Robert, Lynn Henry, Gao Fenghua, Wang Qizhi, Zhang Shiqing, Li Rui, Sun Liqian, Xia Congcong, Xiong Chenglong, Zhang Zhijie, Jiang Qingwu
Department of Epidemiology and Biostatistics, School of Public Health, Fudan University, Shanghai; Key Laboratory of Public Health Safety, Ministry of Education, Shanghai; Laboratory for Spatial Analysis and Modeling, School of Public Health, Fudan University, Shanghai.
Geospat Health. 2015 Jun 3;10(1):324. doi: 10.4081/gh.2015.324.
Schistosomiasis mapping using data obtained from parasitological surveys is frequently used in planning and evaluation of disease control strategies. The available geostatistical approaches are, however, subject to the assumption of stationarity, a stochastic process whose joint probability distribution does not change when shifted in time. As this is impractical for large areas, we introduce here the sandwich method, the basic idea of which is to divide the study area (with its attributes) into homogeneous subareas and estimate the values for the reporting units using spatial stratified sampling. The sandwich method was applied to map the county-level prevalence of schistosomiasis japonica in Anhui Province, China based on parasitological data collected from sample villages and land use data. We first mapped the county-level prevalence using the sandwich method, then compared our findings with block Kriging. The sandwich estimates ranged from 0.17 to 0.21% with a lower level of uncertainty, while the Kriging estimates varied from 0 to 0.97% with a higher level of uncertainty, indicating that the former is more smoothed and stable compared to latter. Aside from various forms of reporting units, the sandwich method has the particular merit of simple model assumption coupled with full utilization of sample data. It performs well when a disease presents stratified heterogeneity over space.
利用寄生虫学调查获得的数据进行血吸虫病绘图，常用于疾病控制策略的规划和评估。然而，现有的地理统计方法需要满足平稳性假设，平稳性是一种随机过程，其联合概率分布在时间上移动时不会改变。由于这对于大面积区域来说不切实际，我们在此引入三明治法，其基本思想是将研究区域（及其属性）划分为同质子区域，并使用空间分层抽样估计报告单位的值。基于从样本村收集的寄生虫学数据和土地利用数据，应用三明治法绘制了中国安徽省日本血吸虫病的县级流行率图。我们首先使用三明治法绘制县级流行率图，然后将我们的结果与块克里金法进行比较。三明治估计值范围为0.17%至0.21%，不确定性较低，而克里金估计值范围为0至0.97%，不确定性较高，这表明前者比后者更平滑、更稳定。除了各种形式的报告单位外，三明治法具有模型假设简单且能充分利用样本数据的特殊优点。当一种疾病在空间上呈现分层异质性时，它表现良好。
