Partitioning of the Reference Group

It may also be necessary to define partitioning criteria for the subclassification of the set of selected reference individuals into more homogeneous groups (Box 16-2). We shall return in later sections to the question of determining when stratification of the reference sample group is necessary and justified. The number of partitioning criteria should usually be kept as small as possible to obtain sufficient sample sizes to derive valid estimates. 

Age and gender are the most frequently used criteria for subgrouping because several analytes vary notably among different age and gender groups (see Chapter gg 

Several preanalytical factors influence the values of biological quantities, such as the concentration of components in 

Physiological Factors Stage ill menstrual cycle Stage in pregnancy Physical condition 

Preanaiyticai standardization of the preparation of individuals before specimen collection, the procedure of specimen collection itself, and the handling of the specimen before analysis may eliminate or minimize bias or variation from these factors. This reduces biological noise that might otherwise conceal important biological signals of disease, risk, or treatment effect. 

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