1) reproducibility of research results;
2) measurement accuracy;
3) stability of results obtained using a specific method over time and with respect to various disturbances (extraneous variables).
In psychodiagnostics, test–retest reliability is distinguished as the stability of results between initial and repeated testing, and internal reliability as the consistency of each test item with the overall result, reflecting the measurement capacity of an individual item or equivalent test form in relation to the studied trait. Reliability characterizes tests of traits, but not states.