What is a primary threat to internal validity related to participant effects over time?

Maturation, or the passage of time, is considered a primary threat to internal validity because it refers to changes that occur within participants as they grow older or due to the passage of time, which can influence the outcomes of a study. As participants experience natural development or changes in their environment, these factors can lead to variations in their responses independent of any treatment or intervention being studied.

For example, if a study is examining the effects of a particular social work intervention on behavior over several weeks, the natural growth and changes in the participants can confound the results, making it difficult to determine whether any observed changes in behavior are truly due to the intervention or just a result of normal maturation processes. This can lead to biased conclusions about the effectiveness of the intervention and undermine the internal validity of the research findings.

In contrast, effects such as testing effects generally relate to the influence of repeated measurements on participant performance rather than changes over time. Ambiguity of direction of causation pertains to challenges in establishing a clear cause-and-effect relationship between variables. Diffusion of intervention methods refers to the spread of an intervention's techniques across groups, which may also affect outcomes but does not directly relate to changes within participants over time.