3.using a reversed-treatment control group: a NR experiment that has a pretest and two different treatments w/ a posttest. the reversed-treatment design can have a special construct validity advantage. the causal construct must be rigorously specified and manipulated to create a sensitive test in which one version of the cause affects one group one way, whereas its conceptual opposite affects another group the opposite way. interpretation of this design depends on producing two effects with opposite signs. it therefore assumes that little historical or motivational change would be taking place. when change is differential across treatments but in the same direction, results are less interpretable, because their relationship to a no-treatment control group is unknown. also, in many contexts, ethical and practical considerations prevent using a reversed-treatment. most treatments have ameliorative and prosocial goals, but a conceptually opposite treatment might be harmful.