The key issue in judging whether a study using a nonequivalent comparison groups design achieves a credible degree of internal validity is the extent to which its authors provide a persuasive case that the groups being compared are really comparable.

Question

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The internal validity of a nonequivalent comparison groups design depends on how well the groups are matched or comparable, as this affects the ability to attribute differences in outcomes to the treatment rather than pre-existing differences.

The Key Issue in Judging Whether a Study Using a Nonequivalent