## Classical Test Theory and Reliability

Classical test theory gives the foundations of the basic true-score model, as discussed in Chapter 2. In this chapter, we will first go into some properties of the classical true-score model and define the basic concepts of reliability and standard error of measurement (Section 3.2). Then the concept of parallel tests will be discussed. Reliability estimation will be considered in the context of parallel tests (Section 3.3). Defining the reliability of measurement instruments is theoretically straightforward; estimating reliability, on the other hand, requires taking into account explicitly the major sources of error variance. In Chapter 4, the most important reliability estimation procedures will be discussed more extensively.