this effect, and data are collected only after performance has stabilized. A retest score can also be influenced by a subject's effort to improve on the first score. This is especially relevant for variables such as strength, where motivation plays an important role. Researchers may not let subjects know their first score to control for this effect. It is also possible for the characteristic being measured to be changed by the first test. A strength test might cause pain in the involved joint and alter responses on the second trial. Range of motion testing can stretch soft tissue structures around a joint, increasing the arc of motion on subsequent testing. When the test itself is responsible for observed changes in a measured variable, the change is considered a testing effect. Oftentimes, such effects will be manifested as systematic error, creating consistent changes across all subjects. Such an effect will not necessarily affect reliability coefficients, for reasons we have already discussed