What does a treatment effect refer to in experimental research?

A treatment effect in experimental research refers to the difference in outcomes between the experimental group, which receives the treatment, and the control group, which does not. This concept is central to determining the efficacy of an intervention or treatment. By comparing the results of these two groups, researchers can isolate the impact of the treatment itself, allowing them to infer whether any changes observed can be attributed specifically to the treatment rather than other variables.

In essence, the treatment effect quantifies how much the treatment has influenced the outcome measures of interest, helping to establish a causal relationship. This is foundational to experimental design because it provides evidence for the effectiveness of a treatment or intervention, guiding future practices and research.