Measurement theory which consists of a set of assumptions about the relationships between actual or observed test scores and the factors that affect the scores. It is used for measuring and managing test and item performance data. In contrast to item response theory, it comprises a set of more traditional psychometric methods. In CTT, the global level ability of a test taker depends on the overall test difficulty and vice-versa. There is no way to obtain parameters of each test item or the level ability of the test taker in each item on a scale performance continuum as in IRT and Rasch models.