Test Reliability—Basic Concepts Samuel A. Livingston Educational Testing Service, Princeton, New Jersey. This correlation is known as the test-retest-reliability coefficient, or the coefficient of stability. a reliability coefficient of .70 or higher. For good classroom tests, the reliability coefficients should be .70 or higher. Again, an Alpha of … Reliability coefficients are variance estimates, meaning that the coefficient denotes the amount of true score variance. 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. Cronbach's Coefficient Alpha has become the most popular way of reporting estimates of the reliability of psychological measures. Ideally, score reliability should be above 0.80. In reality, all tests have some error, so reliability is never 1.00. 4 Difficulty Item Difficulty represents the percentage of students who answered a test item correctly. Typically the measurement of reliability is reflected in what is called a reliability coefficient. 2.3. 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. The correlation between one set of observations with the second, then, provides a reliability coefficient. Technically speaking, Cronbach’s alpha is not a statistical test – it is a coefficient of reliability (or consistency). This means that low item Reliability coefficients of .6 or .7 and above are considered good for classroom tests, and .9 and above is expected for professionally developed instruments. Coefficients in the range 0.80-0.90 are considered to be very good for course and licensure assessments. 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. Reliability coefficients range from 0.00 to 1.00. Reliability coefficients range from 1.00 (which is highest) to 0.00 (which is lowest). ¨ 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). The reliability of a test is indicated by the reliability coefficient. (Internal 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). C. Reliability Standards. It is January 2018 Corresponding author: S. A. 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