Study Objectives and General 

 Sampling Design 



Note that the second and third steps above depend on information 

 developed as part of the characterization of the exposed population 

 (see Exposed Population Analysis below). Also, practical limitations 

 of field sampling may dictate compromises in the sampling design. For 

 example, use of equal sample sizes is generally recommended because 

 statistical analysis of data sets with unequal sample sizes may be 

 difficult or unnecessarily complex. However, collection of equal num- 

 bers of replicate samples for each treatment (or stratum) may be 

 impractical if both dominant and rare species are to be sampled at a 

 series of harvest locations with a broad range of harvest yields. 

 Depending on the specific objectives and corresponding study design, 

 a series of statistical analyses rather than a single test may be ap- 

 propriate. 



Detailed guidance on sampling strategies is provided by Phillips 

 (1980), Green (1979), Tetra Tech (1985b,c; 1986b), Phillips and Segar 

 (1986), and Gilbert (1987). Much of the guidance provided in the 

 following sections incorporates the suggestions of these authors. 



The statement of objectives is a critical step in the study design process, 

 since specification of other design elements depends on the survey 

 objectives. The study objectives must in turn relate to the objectives of 

 the exposure assessment in which the data will be used. The relation- 

 ships between study objectives and general features of a sampling 

 design are addressed in the next section. 



Specific objectives of a chemical residue study should be defined to 

 ensure collection of appropriate data for the exposure assessment. 

 Different objectives may require radically different sampling designs. 

 Although the primary objective of a field study may be to estimate the 

 mean concentrations of specified chemical contaminants in edible 

 tissues of harvested species, it may be necessary to specify additional 

 objectives to meet the needs of exposure assessment or risk manage- 

 ment. For instance, statistical discrimination among mean con- 

 taminant concentrations in samples from different harvest areas, 

 seasons, or species maybe desired. Such information might be needed 

 to manage relative risks among harvest areas and to impose fisheries 

 closures on a site-specific basis. 



Example Objectives-Some examples of objectives for exposure assess- 

 ments paired with appropriate bioaccumulation survey objectives are 

 given below. These objectives are provided to illustrate the ways in 

 which the elements of a bioaccumulation study design depend on the 

 exposure assessment objectives. They are not intended to be recom- 

 mended objectives for an actual exposure assessment. In these ex- 

 amples, the bioaccumulation study design involves specifically the 

 measurement of chemical residues in edible tissues of fishery species. 

 Information on the exposed population, including an analysis of their 

 dietary habits (e.g., fisheries species consumed, food preparation 

 method, and consumption rate), is discus.sed later (see Exposed 

 Population Analysis). Such information may influence the objectives 

 of the exposure assessment and the bioaccumulation survey. 



32 



