ABSTRACT
Chapters 17–19 describe how to evaluate the merit or validity of a research study. We use the term research validity when discussing the merit of a whole study to distinguish it from validity of the measurement of a variable. Based on the work of Cook and Campbell (1979), research validity is divided into four components: (a) measurement reliability and statistics, (b) internal validity, (c) overall measurement validity of the constructs, and (d) external validity. In this chapter the focus is on internal validity.
