Strategies for Selection of Reference Individuals

Several methods have been suggested for the selection of reference individuals. Table 16-1 shows three pairs of concepts that may be used to describe a sampling scheme. The concepts of each pair are mutually exclusive. For example, the sampling is either direct or indirect. One may, however, combine one concept from several pairs to obtain a more exact description. For example, the selection may be direct, a posteriori, and nonrandom. 

The merits and disadvantages of these strategies are described in the foHowing sections. It is not possible to recommend one sampling scheme that is superior in all respects and applicable to all situations. One must choose the optimal approach for a given project and state clearly what has been done. 

Direct selection of reference individuals (see Table 16-1) is the only method that agrees with the concept of reference 

A direct method (see above) in which individuals are selected for specimen collection and analysis if they fulfill defined inclusion criteria. 

A direct method using an already existing database containing both analysis results and information on a number of individuals. Values of 

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