Regression artifacts are less of a problem when participant populations differ than when participants are randomly assigned to groups.

Question

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Regression artifacts, or regression to the mean, are more problematic when participant populations differ because pre-existing differences can confound the interpretation of change, making it harder to attribute changes to the intervention rather than to natural variation or initial group differences. Random assignment helps to minimize pre-existing differences between groups, thereby reducing the impact of regression artifacts.

Regression Artifacts Are Less of a Problem When Participant Populations