A measure of consistency and the ability to repeat experiment and get similar results on another occasion

Internal reliability: Whether a measure is consistent within itself when tested – eg a questionnaire generating similar results with all participants. Tested through interobserver reliability – comparing with different observers using a checklist, or using Spearman’s rho test.

External reliability: A measure of consistent results on similar people on different occasions. Tested using the test-retest method – compare the results of the test at one time with results from another time using similar participants.