2.3. It is It is denoted by the letter "r," and is expressed as a number ranging between 0 and 1.00, with r = 0 indicating no reliability, and r = 1.00 indicating perfect reliability. ¨ A reliability coefficient can range from a value of 0.0 (all the variance is measurement error) to a value of 1.00 (no measurement error). Cronbach's Coefficient Alpha has become the most popular way of reporting estimates of the reliability of psychological measures. This is unlike a standard correlation coefficient where, usually, the coefficient needs to be squared in order to obtain a variance (Cohen & Swerdlik, 2005). Reliability coefficients of .6 or .7 and above are considered good for classroom tests, and .9 and above is expected for professionally developed instruments. The correlation between one set of observations with the second, then, provides a reliability coefﬁcient. A good rule of thumb for reliability is that if the test is going to be used to make decisions about peoples lives (e.g., the test is used as a diagnostic tool that will determine treatment, hospitalization, or promotion) then the minimum acceptable coefficient alpha is .90. a reliability coefficient of .70 or higher. (Internal For good classroom tests, the reliability coefficients should be .70 or higher. This means that low item Technically speaking, Cronbach’s alpha is not a statistical test – it is a coefficient of reliability (or consistency). Post hoc power analysis confirmed previous power analysis, that is, despite the small sample size, an excellent power was found for the observed interobserver reliability coefficients (power range, 0.93-1.00). High reliability coefficients are required for standardized tests because they are administered only once and the score on that one test is used to draw conclusions about each student’s level on the trait of interest. Cronbach’s alpha can be written as a function of the number of test items and the average inter-correlation among the items. Test Reliability—Basic Concepts Samuel A. Livingston Educational Testing Service, Princeton, New Jersey. Reliability coefficients are variance estimates, meaning that the coefficient denotes the amount of true score variance. Coefficients in the range 0.80-0.90 are considered to be very good for course and licensure assessments. This correlation is known as the test-retest-reliability coefficient, or the coefficient of stability. Reliability coefficients range from 0.00 to 1.00. C. Reliability Standards. Reliability study designs and corresponding reliability coefﬁcients To estimate test-score reliability, at a minimum one needs at least two observations (scores) on the same set of persons (Tables 2a and 2b). No learning effect was found when comparing the results of the second measurement with the first measurement (P>.05). 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