A Review of Composite Sampling Methods

Abstract

A composite is formed by collecting multiple sample units and combining them in their entirety or in part, to form a new sample. The sample units that make up the composite may retain their integrity or be homogenized through physical processes such as ball milling, sieving, shaking, or centrifuging. One or more subsequent measurements are taken on the composite and the information on the sample units is lost. This counterintuitive loss of information has fueled opposition to composite sampling, while the methodology's adherents find their motivation in its ability to reduce measurement costs for many classes of problems. This article reviews the scientific literature related to the development of composite sampling methods. The literature on compositing exists only as a compendium derived from disparate disciplines in which terms such as compositing, group screening, pooling, and weighing designs are used. The goal of this review is to synthesize this body of literature. The articles reviewed are limited to those that offer original applications or methodologies. A novel application in numerical regularization, is illustrated using data from an environmental investigation into mercury contamination at a waste disposal site in New Mexico. What is unusual about these data is the existence of measurements at both the composite and sample unit levels, thus allowing an opportunity to evaluate estimates based on composite sampling methods.