The reliability of criterion referenced tests, which are often used to evaluate health education programs, may be conceptualized in different ways. Classical conceptualizations of test reliability have limited usefulness when applied to health-related criterion referenced tests. When a cutting score is set, test reliability can be represented as the consistency of mastery versus nonmastery classifications; the Kappa index may also be used. When a cutting score is not set, the size of the standard error of measurement of a domain score estimate reflects test reliability. Five simple mathematical formulas that estimate measurement error for criterion referenced tests are presented. Measurement error may be used to compute confidence intervals for domain score estimates and for the cutting score. (Author/GDC)