The use of ranked set sampling in spray deposit assessment.

Summary Ranked set sampling is a modification of simple random sampling that is intended to give improved precision. The method involves selecting small sets of samples and ranking them, for example visually. A s ingle sample from each set is then measured. The performance of the method in estimating spray deposits on the leaves of apple trees was assessed. Leaves s prayed with a fluorescent tracer dye were ranked visually under ultra-violet light. Despite errors in ranking, ranked set sampling improved the precision of estimating the mean percentage of the upper leaf surface covered with d eposit, and the total deposit on the upper surface of the leaf. However, when the additional overhead associated with ranked set sampling was taken into account, the method was more efficient than simple random sampling only for estimating total deposit.