ABSTRACT
The use of auxiliary information was introduced in Chapter 3 in connection with the selection of samples. In Example 3.20, an easily measured tree attribute, diameter .x/, was known for all elements in the population of red oak trees, whereas the attribute of interest, the aggregate volume in the boles of the trees .y/, was estimated from a systematic sample. The trees were ordered from smallest to largest for the systematic selection. This proved efficient because bole volume, y, is correlated with diameter, x, so any sample which tends to span the range of diameters also tends to span the range of volumes. Elsewhere in Chapter 3 we described (a) how to select units with replacement with probability proportional to an auxiliary variate, x, and (b) how to use an auxiliary variate to select units systematically with unequal probability.
