ABSTRACT
Measurement reliability and measurement validity are two parts of overall research validity, the quality of the whole study. What is reliability? Reliability refers to consistency of scores on a particular instrument. It is incorrect to state that a test is reliable. Instead, we are interested in the scores from the test, taking into account the sample that took the test. For example, there may be strong evidence for reliability for adults, but scores of depressed adolescents on this test may be highly inconsistent. When we use tests or other instruments to measure outcomes, we need to make sure that they provide us with consistent data. If our outcome measure is not reliable, then we cannot accurately assess the results of our study.
