Refers to the accuracy and consistency of a measuring tool. A measure is reliable when an individual remains nearly the same in repeated measurements. Reliability is measured by reliability coefficient and the estimation of rkliability can be done statistically. How to estimate the degree of reliability?
a) Coefficient of Stability shows consistency of performance on a test over a period of time. It is based on the correlation between performances on initial test and retest after a distinct interval. That is, it involves repetition of the same test. A test may be reliable even though it may not be valid. A valid test is usually reliable.
b) Coefficient of Equivalence shows consistency of performance on different forms of a test. It is based on the correlation between performances on the different .forms administered at nearly the same time. That &, a second equivalent form of the test is administered.
c) Coeflcient of Internal Consistency shows consistency of performance on different parts or items of the test taken at a single sitting. This coefficient is usually computed by "split-half' correlation (e.g. Sperman-Brown formula), or by using Kuder-Richardson formula. That is, the analysis involves subdivision of the test into two or more equivalent fractions.