Measurement is the area of quantitative social science that is concerned with ascribing numbers to individuals in a meaningful way. Measurement is distinct from statistics, though measurement theories are grounded in applications of statistics. Within measurement there are several theories that allow us to talk about the quality of measurements taken. Classical test theory (CTT) can arguably be described as the first formalized theory of measurement and is still the most commonly used method of describing the characteristics of assessments. With test theories, the term test or assessment is applied widely. Surveys, achievement tests, intelligence tests, psychological assessments, writing samples graded with rubrics, and innumerable other situations in which numbers are assigned to individuals can all be considered tests. The terms test, assessment, instrument, and ...