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A term attributed to Campbell (1957) and Campbell and Stanley (1963), with a more extensive description by Cook and Campbell (1979) and Shadish, Cook, and Campbell (2002), referring to the use of designs where random assignment of participants to comparison groups is not used to structure the comparison groups. Sometimes random assignment is not possible because participants are already in intact groups or they may have a common characteristic that is not under the control of the researcher (e.g., gender, political preference, marital status). There is a controlled or explicit independent variable or treatment manipulation, as is the case in experimental research. There are recognized examples of these designs, each having a variety of design arrangements. Nonequivalent group designs compare results on a dependent variable ...