ABSTRACT
In the present chapter, we address the broad topic of measurement precision. After some general observations about the status of reliability in measurement and research, we turn to a consideration of different types and sources of measurement errors, and how they relate to conceptions and definitions of reliability. Classical test theory is then presented as an example of reliability theories that have been advanced and as a means of introducing fundamental concepts of reliability. This is followed by a review of some of the most common approaches to the estimation of reliability, with an emphasis on internal-consistency estimates, in the context of which numerical examples are analyzed by hand and/or through the use of a computer program. Considerations in the selection of a reliability estimate are then reviewed. The chapter concludes with some selected topics, among which are standards for reliability, relation between reliability and validity, effects of unreliability on statistical estimation.
