Cost analysis of composite sampling for classification

When an environmental sampling objective is to classify all the sample unit s as contaminated or not, composite sampling with selective retesting can s ubstantially reduce costs by reducing the number of units that require dire ct analysis. The tradeoff, however, is increased complexity that has its ow n hidden costs. For this reason, we propose a model for assessing the relat ive cost, expressed as the ratio of total expected cost with compositing to total expected cost without compositing (initial exhaustive testing). Expr essions are derived for the following retesting protocols: (i) exhaustive, (ii) sequential and (iii) binary split. The effects of both false positive and false negative rates are also derived and incorporated. The derived expressions of relative cost are illustrated for a range of val ues for various cost components that reflect typical costs incurred with ha zardous waste site monitoring. Results allow those who are designing sampli ng plans to evaluate if any of these compositing/retesting protocols will b e cost effective for particular applications.