Wilson P D
University of Maryland Medical School, Baltimore 21201.
Stat Med. 1988 Mar;7(3):417-22. doi: 10.1002/sim.4780070307.
Consider a variable whose expected value distributes among individuals in a population, and which also has an important component of within-individual variance. In a screening study that involves repeated observations only for those individuals whose initial observation exceeds an arbitrary cutoff point, the usual estimator of within-individual variance is biased. Assuming normality and independence, this note gives the derivation of the expected value of the estimator and uses it to obtain an unbiased estimator. The results generalize to the bivariate case that involves selection on only one variable of the pair. A companion paper provides an example with use of blood pressure.
考虑一个变量，其期望值在总体中的个体间分布，并且该变量在个体内部方差方面也有一个重要组成部分。在一项筛查研究中，仅对那些初始观测值超过任意截断点的个体进行重复观测，个体内部方差的常用估计量是有偏的。在假设正态性和独立性的情况下，本笔记给出了该估计量期望值的推导，并利用它得到一个无偏估计量。结果推广到仅对二元组中的一个变量进行选择的二元情况。一篇配套论文给出了一个使用血压的例子。
