ABSTRACT
Accuracy—aka validity—is a centrally important concept to measurement. This unit covers validity, starting with distinguishing internal and external validity. The three main types of measurement validity (construct, content, and criterion validity) are presented in this unit. Additionally, threats to validity are presented in a format that emphasizes the way that many threats may affect both internal and external validity. Specific threats discussed include observer effects, mortality, sensitization, regression toward the mean, history, floor and ceiling effects, and selection bias, among others.
