Estimating Population Size With Link-Tracing Sampling

We present a new design and method for estimating the size of a hidden population best reached through a link-tracing design. The design is based on selecting initial samples at random and then adaptively tracing links to add new members. The inferential procedure involves the Rao–Blackwell theorem applied to a sufficient statistic markedly different from the usual one that arises in sampling from a finite population. The strategy involves a combination of link-tracing and mark-recapture estimation methods. An empirical application is described. The result demonstrates that the strategy can efficiently incorporate adaptively selected members of the sample into the inferential procedure. Supplementary materials for this article are available online.