How does testing effects threaten internal validity?

Testing effects can threaten internal validity because they can influence how participants respond based on their exposure to the testing instrument itself. When participants are repeatedly tested, they may become familiar with the questions or tasks, or they may learn how to respond in ways that align with what they think the researchers expect. This familiarity can lead to changes in their responses that are not due to the intervention being studied but rather to the effects of prior exposure to the test. Such alterations in responses can obscure the true relationship between the variables being investigated, making it difficult to draw valid conclusions about the cause-and-effect dynamics in the research.

This phenomenon impacts the integrity of the data collected, as any observed changes may reflect the influence of prior testing instead of the effectiveness of the treatment or intervention being evaluated. Therefore, recognizing and controlling for testing effects is essential for maintaining the internal validity of research findings.