Reliability refers to the extent to which a test or other instrument is consistent in its measures. For example, a weight scale can be judged reliable if measures for a 25-pound weight do not vary over time or change for subsequent weightings. Reliability is an important concept in science. If a test is not reliable, we cannot find the answers to our questions. Imagine placing a 25-pound weight on a scale and getting a different answer every time. What purpose would the scale serve? In fact, we most likely would question if indeed the scale is measuring weight or something entirely different. Unreliability would prohibit us from reporting our findings simply because they are not reliable.