Under ideal circumstances, individual test results would be referenced to the performance of the entire collection of individuals (target population) for whom the test is intended. However, it is rarely feasible to measure performance of every member in a population. Accordingly, tests are developed through sampling procedures, which are designed to estimate the score distribution and characteristics of a target population by measuring test performance within a subset of individuals selected from that population. Test results may then be interpreted with reference to sample characteristics, which are presumed to accurately estimate population parameters. Most psychological tests are norm referenced or criterion referenced. Norm-referenced test scores provide information about an examinee's standing relative to the distribution of test scores found in an appropriate peer comparison group. Criterion-referenced tests yield scores that are interpreted relative to predetermined standards of performance, such as proficiency at a specific skill or activity of daily life.
When a test is intended to yield information about examinees' standing relative to their peers, the chief objective of sampling should be to provide a reference group that is representative of the population for whom the test was intended. Sample selection involves specifying appropriate stratification variables for inclusion in the sampling plan. Kalton (1983) notes that two conditions need to be fulfilled for stratification: (a) The population proportions in the strata need to be known, and (b) it has to be possible to draw independent samples from each stratum. Population proportions for nationally normed tests are usually drawn from Census Bureau reports and updates.
The stratification variables need to be those that account for substantial variation in test performance; variables unrelated to the construct being assessed need not be included in the sampling plan. Variables frequently used for sample stratification include the following:
Was this article helpful?