chapter  8
26 Pages

Test Dimensionality: Richard Tate

Test dimensionality, roughly defined as the minimum number of examinee abilities

measured by the test items, is a unifying concept that underlies some of the most central

issues in the development and use of large-scale tests. To illustrate, consider four

practical concerns that are prominent in the Standards for Educational and Psychological

Testing (AERA, APA, NCME, 1999). First, the content-related aspect of test validity

requires consistency of the test dimensionality and the target test content structure,

suggesting that the usual logical comparison of the test items with the test specification

plan should be supplemented with an empirical analysis of test structure. In addition,

dimensionality-related tools are also essential in the search for possible construct-

irrelevant factors that may threaten the validity of the test. Second, the standard methods

of computing the score reliability and precision assume that the test is

unidimensional-an assumption that is almost always violated to some extent. Thus, the

test developer must ask whether the estimated reliability accurately represents the actual

reliability despite the violations of unidimensionality. When there is a serious lack of

robustness to such violations, alternative methods of estimating reliability can be sought.