Measurement theory is a branch of psychology and psychometrics that focuses on the development and evaluation of measures and scales used in psychological research. It deals with the theoretical foundations of measurement, including the concept of reliability (consistency of measurement) and validity (accuracy of measurement). Measurement theory also addresses issues such as scaling, item response theory, and factor analysis, as well as the development of new measurement models and techniques. The goal of measurement theory is to ensure that measures used in research are accurate, reliable, and valid in order to produce meaningful and trustworthy results.