A non-equivalent group design is one where the assignment of participants to groups is not controlled by the investigator. When group assignment is not controlled there is a significant threat to internal validity. Since group assignment is not random, there is a chance that the groups are not similar.

What is nonequivalent control group designs?

a quasi-experimental design in which the responses of a treatment group and a control group are compared on measures collected at the beginning and end of the research.

What is a nonequivalent control group design example?

Imagine, for example, a researcher who wants to evaluate a new method of teaching fractions to third graders. ... This design would be a nonequivalent groups design because the students are not randomly assigned to classes by the researcher, which means there could be important differences between them.