Pub. date: 2006 | Online Pub. Date: September 15, 2007 | DOI: 10.4135/9781412939584 | Print ISBN: 9780761930877 | Online ISBN: 9781412939584| Publisher:SAGE Publications, Inc.About this encyclopedia
Measurement, Theories of
Measurement is the process of estimating psychometric properties of variables or constructs. There are a number of measurement theories that represent different assumptions about and approaches to the estimation process, including the classical test theory (CTT), the generalizability theory (G-theory), the congeneric theory, and the item response theory (IRT). The most influential theory in psychometric measurement is the CTT. The theory relies on the test score to measure a person's ability or other psychometric properties. Central to the theory is the concept of reliability, first used by Charles Spearman in 1904. According to Spearman, the observed score of a variable or construct consists of two separate components: the true score and the error of measurement. The true score represents the perfect measurement of a construct, for instance, the true ability of a person to accomplish a task. In theory, if a person takes the same test an infinite number of ...