“…According to Cook and Campbell, quasi-experimental designs are &dquo;not in any way qualitatively different from the ones we labeled 'generally uninterpretable,' they merely make it possible to rule out more threats to internal validity&dquo; (1979, p. 103). Six of the reviewed studies were classified as quasiexperimental designs: five of them (Adams & Sherwood, 1979;Boss & McConkie, 1981;Cohen & Turney, 1978-Phase 1;Nadler, Cammann, & Mervis, 1980;and Paul & Gross, 1981) utilized nonequivalent control group designs, and one (Porras & Wilkins, 1980), used a multiple time-series design. For the most part, these studies overcame many of the weaknesses found in the studies utilizing preexperimental designs; however, selection interactions and selection by treatment interaction were still generally judged to be plausible threats to their validity.…”