Quasi-experimental design

In evaluation research, quasi-experimental design studies are different from experimental design studies in that participants are not randomly assigned to treatment and control groups.   While a quasi-experimental design typically uses comparison groups, random assignment is not used in this design because it is often impractical or impossible to do so.  To minimize threats to validity in quasi-experimental design studies, researchers can try to account for pre-existing factors (e.g., pretest knowledge or attitudes) that could affect the outcome differences between treatment and comparison groups.