nonequivalent groups design

n. A quasi-experimental research design in which individuals are not randomly assigned to groups, and existing or convenient groups which differ on an independent variable are selected, such as those in two hospitals or schools, or in different cultures. The groups are measured at the beginning and end of the treatment and compared with each other, but the comparisons are suspect as there are likely to be differences between the groups before the experiment which have an effect on the dependent variable, making group comparisons difficult to interpret.