Sampling designs for xerophthalmia prevalence surveys.
Sampling designs for xerophthalmia prevalence surveys.
复制标题
干眼症患病率调查的抽样设计。
DOI：
10.1093/ije/26.5.1041
复制
发表时间：
1997
影响因子：
7.7
通讯作者：
WestJr,KP
中科院分区：
文献类型：
--
作者：
Katz,J;Yoon,SS;Brendel,K;WestJr,KP
背景：本研究的目的是在估计干眼症患病率时，估计与扩大免疫规划（EPI）抽样设计相关的偏倚和设计效应，并估计与EPI相关的在所选群集内旅行距离方面的节省。方法：利用尼泊尔萨拉希地区40个干眼症病房的干眼症调查地图，对EPI抽样策略进行计算机模拟。将固定簇大小为7、10、15、20和25的样本进行比较。使用EPI设计的估计患病率与40个病房的真实患病率进行比较，以估计偏倚。采用EPI抽样下的方差与固定簇大小的分层随机抽样（SRS）的方差之比来估计设计效果。EPI也被修改了，增加了所选房屋与最近邻居之间的距离，在所选房屋之间跳过1-4所房屋。与EPI相比，使用SRS的聚类内旅行距离之间的差异被权衡了偏差和增加的方差。结果：干眼症患病率为2.8%。EPI设计高估了干眼症患病率0.27%至1.16%。病房内EPI聚类抽样的设计效果在0.73 ~ 1.35之间。偏差和设计效应都与家庭之间的距离或集群大小无关。对于聚类大小为7或10的EPI设计，病房内移动的距离总是较小。如果在选定的房屋之间有两个或更多的房屋，那么在集群大小从15到25的设计中，没有节省旅行距离。对于15或更少的固定簇大小，使用最近或次最近邻居的EPI抽样设计在最小化行进距离和均方误差方面比SRS更好。结论：最佳方法的选择需要考虑集群的密度、集群之间的出行难度以及集群内的出行成本。基于某些假设，除非病房之间的旅行时间超过2天，否则每组15名儿童的EPI将比检查选定病房的所有儿童更受欢迎。
BACKGROUND: The purpose of this study was to estimate the bias and design effects associated with the Expanded Program on Immunization's (EPI) sampling design when estimating xerophthalmia prevalence, and to estimate the savings associated with EPI in terms of distance travelled within selected clusters. METHODS: Computer simulation of the EPI sampling strategy was done using maps from a xerophthalmia survey of 40 wards in Sarlahi district, Nepal. Samples of fixed cluster sizes of 7, 10, 15, 20 and 25 were compared. The estimated prevalence using the EPI design was compared with the true prevalence in the 40 wards to estimate the bias. The design effect was estimated by taking the ratio of the variance under EPI sampling to that of stratified random sampling (SRS) with fixed cluster sizes. The EPI was also modified by increasing the distance between selected houses from nearest neighbour to skipping 1-4 houses between selected ones. The difference between the distance travelled within clusters using SRS compared with EPI was weighed against the bias and increased variance. RESULTS: The prevalence of xerophthalmia was 2.8%. The EPI design overestimated xerophthalmia prevalence by between 0.27% and 1.16%. The design effects of EPI cluster sampling within wards varied between 0.73 and 1.35. Neither the bias nor the design effect was related to distance between households or cluster size. Distance travelled within wards was always less for EPI designs with cluster sizes of 7 or 10. There was no saving in terms of distance travelled for designs with cluster sizes from 15 to 25 if there were two or more houses between selected ones. For fixed cluster sizes of 15 or fewer, the EPI sampling design using nearest or next nearest neighbours is a better choice than SRS in terms of minimizing the distance travelled and the mean square error. CONCLUSIONS: The choice of an optimum method would need to account for the density of clusters and difficulty of travel between clusters, as well as the costs of travel within clusters. Based on certain assumptions, EPI with 15 children per cluster would be favoured over examining all children in selected wards unless the travel time between wards was more than 2 days.