Publication Abstract

Contaminants in marine organisms:pooling strategies for monitoring mean concentrations

M.D. Nicholson and R.J. Fryer

Samplesof marine organisms collected for contaminant monitoring are often pooled before beingchemically analysed. The main reasons for pooling samples are:

1. to obtain a sufficient quantity of tissue to make thechemical analysis possible;
2. to reduce the overall cost of chemical analyses;
3. to improve the precision of the estimated meancontaminant concentration in a population by increasing the sample size without increasingthe number of chemical analyses.

However, there are several questions associated withpooling, including:

• what is an appropriate pooling strategy?
• how should data from pools be statisticallyanalysed?
• how should results derived from pooled data beinterpreted?

This document is an introduction to thestatistical aspects of pooling. Unfortunately, it is not possible to consider all thesituations in which pooling might arise, nor to describe the many types of statisticalanalysis that might be appropriate. The scope is too large, and we do not know all theanswers. Here consideration is given to the relatively simple case of estimating the meanconcentration of a contaminant in a population; it shows the typical problems encounteredin devising an appropriate pooling strategy and statistically analysing data from pools.In particular, it shows how the choice of the number of pools and the number ofindividuals in each pool allows a balance to be made of the precision of the estimatedmean concentration against the sampling and analytical costs incurred in obtaining thatestimate.

Reference:

M.D. Nicholson and R.J. Fryer, 1996. Contaminants in marine organisms: pooling strategiesfor monitoring mean concentrations. ICES Techniques in Marine Environmental Sciences, 18:30pp.