![]() The goal of test developers is to minimize errors in our measurements to optimize their precision. The random variation we might observe in repeated measurements we refer to as error, which is the converse concept to reliability. Unless there is an identifiable factor that should influence dramatic changes, we would expect comparable results across repeated test administrations. It might fluctuate slightly from day to day, but large swings in the results would indicate that the instrument has become unreliable. Unless I was doing something intentional to reduce or increase my weight, I would expect approximately the same number, within a narrow range, to appear. Our expectation of that scale is a consistent number will display on the digital read-out each time it’s stepped on. Imagine a measuring device we are all (perhaps painfully) familiar with - a common bathroom scale. Under this analogy of measurement, we can define reliability as the consistency or comparability of repeated measurements of the same or like subjects (i.e., the focus of the measurement, or the test candidate). In explaining the activity of testing to non-testing folks, I have often found it helpful to conceptualize testing as a measurement activity. Along with validity and fairness, reliability is a foundational principle of assessment. ![]()
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