Psychological assessment is dedicated to measuring psychological characteristics such as personality traits, attitudes, and abilities.

Various measures are used to this end, including questionnaires, performance tests, interviews, behavioral observation and laboratory tasks. Their administration and scoring correspond to the state of evidence-based research.

Psychological assessment plays an important role in many fields of applied psychology, like in educational, organizational, clinical, and forensic psychology. To ensure high quality of diagnostic decisions, procedures are constantly evaluated and improved in accordance with relevant theories and with regard to the requirements of the application disciplines.

Psychological assessment therefore lies at the intersection of (statistical) methods, psychological theories, and psychological applications.

Research methods deal with how to design and evaluate empirical studies, so to derive reliable and informative findings. 

This includes research designs, survey methods, measurement theories, as well as tailored quantitative analysis techniques. To this end, statistical models are developed or applied, and their fit to the data is evaluated. 

An important goal is to find out to which extent sample data can be used to infer psychological principles and mechanisms. Research methods, thus, help test psychological theories as well as to evaluate the effectiveness of social projects or clinical interventions.

Research methods overlap with psychological assessment in the area of test theory and test construction. And it is also relevant to test the reliability and validity of diagnostic tests.