Research and Evaluation (2%)
.. In statistics, reliability is the consistency of a measure. A measure is said to have a high reliability if it produces consistent results under consistent conditions. For example, measurements of people’s height and weight. Reliability does not imply validity. That is, a reliable measure that is measuring something consistently, may not be measuring what you want to be measuring. Reliability theory shows that the variance of obtained scores is simply the sum of the variance of true scores plus the variance of errors of measurement. The reliability coefficient provides an index of the relative influence of true and error scores on attained test scores. In its general form, the reliability coefficient is defined as the ratio of true score variance to the total variance of test scores. Unfortunately, there is no way to directly observe or calculate the true score, so a variety of methods are used to estimate the reliability of a test. Some examples of the methods to estimate reliability include test-retest reliability, internal consistency reliability, and parallel-test reliability.