While a reliable test may provide useful valid information, a test that is not reliable cannot possibly be valid. A test that is not perfectly reliable cannot be perfectly valid, either as a means of measuring attributes of a person or as a means of predicting scores on a criterion. While reliability does not imply validity, reliability does place a limit on the overall validity of a test. For example, while there are many reliable tests of specific abilities, not all of them would be valid for predicting, say, job performance. That is, a reliable measure that is measuring something consistently is not necessarily measuring what you want to be measured. See also: Validity (statistics) § Reliability Internal consistency reliability, assesses the consistency of results across items within a test.When dealing with forms, it may be termed parallel-forms reliability. This allows inter-rater reliability to be ruled out. Inter-method reliability assesses the degree to which test scores are consistent when there is a variation in the methods or instruments used.Measurements are gathered from a single rater who uses the same methods or instruments and the same testing conditions. Test-retest reliability assesses the degree to which test scores are consistent from one test administration to the next.For example, a person gets a stomach ache and different doctors all give the same diagnosis. Inter-rater reliability assesses the degree of agreement between two or more raters in their appraisals.There are several general classes of reliability estimates: Various kinds of reliability coefficients, with values ranging between 0.00 (much error) and 1.00 (no error), are usually used to indicate the amount of error in the scores.' įor example, measurements of people's height and weight are often extremely reliable. That is, if the testing process were repeated with a group of test takers, essentially the same results would be obtained. Scores that are highly reliable are precise, reproducible, and consistent from one testing occasion to another. 'It is the characteristic of a set of test scores that relates to the amount of random error from the measurement process that might be embedded in the scores. A measure is said to have a high reliability if it produces similar results under consistent conditions: In statistics and psychometrics, reliability is the overall consistency of a measure.

Psychometric reliability