A study includes a pretest that influences the results. What kind of effect does this represent?

In research studies, a pretest can indeed influence the outcomes by altering how participants respond to the subsequent measures. This influence represents a measurement effect. Measurement effects occur when the act of measuring or testing participants impacts their future responses or performance. This can happen if participants become accustomed to the test format, change their behavior as a result of the pretest, or develop new strategies that affect the validity of the results.

In this instance, when the pretest significantly shifts participant attitudes or behaviors, it impacts the reliability and validity of the data gathered after the intervention. The critical factor here is that the pretest itself—even if it is intended to establish a baseline—can create a situation where the latter responses are not purely reflective of the changes brought about by the intervention.

While maturation, selection, and history effects pertain to other factors influencing study outcomes, they do not specifically address the direct impact of a pretest influencing participant responses in a way that skews subsequent results. Maturation refers to internal changes within participants over time, selection affects how participants are chosen for groups, and history effects involve external events occurring during the study that can influence outcomes.