ABSTRACT
Within classical psychometrics, two of the most important aspects of a test are its reliability and its validity. Reliability has been defined as the extent to which the test is effectively measuring anything at all, and validity as the extent to which the test is measuring what it is purported to measure. If a test is unreliable it is impossible for it to be valid, so that it would be a logical impossibility to have a test which was valid but completely unreliable. On the other hand a test can be reliable but invalid.
