ABSTRACT
In this chapter and the next we discuss the reliability and validity of individual measurements or scores from an instrument. The quality of a study depends, in part, on the quality of the design (internal validity) and of the sample (population external validity) as discussed in Chapters 8 and 9. Study quality also depends on the consistency (measurement reliability) and accuracy (measurement validity) of the specic instruments, as discussed in this chapter and Chapter 12. In Chapters 23 and 24, we show how these four quality indicators (and others) can be used to evaluate the overall quality of a study.
