题目
Problem
A researcher believes that the median of a population has changed from its known previous value . The researcher collects a random sample of size 28. She ranks the data and calculates a test statistic using the Wilcoxon signed-rank test. The conclusion of the test carried out at a significance level is that there is not sufficient evidence to support her belief.
Using a normal approximation, find the least possible value of .
[5]
题目中文翻译
一名研究者认为某总体的中位数 已从其已知的先前值 发生改变。研究者收集了一个容量为 28 的随机样本。她对数据进行秩排序，并使用 Wilcoxon signed-rank test 计算检验统计量 。在 显著性水平下进行检验后的结论是，没有足够证据支持她的看法。
使用正态近似，求 的最小可能值。