Second-Order Inclusion Probabilities in Sequential Sampling Without Replacement with Unequal Probabilities
研究了Chao(1982)提出的不等概率无放回顺序抽样方案，给出了二阶包含概率严格为正的充要条件。
Necessary and sufficient conditions for strictly positive second-order inclusion probabilities are given for a sequential sampling scheme proposed by Chao (1982), in which elements are selected without replacement and with unequal probabilities.