Quasi-experimental design

A quasi-experimental design is a research study design that looks a bit like an experimental design but lacks the key ingredient -- random assignment.

Methods may include comparing two similar, but non-random groups (two 2nd grade classrooms, for example) or matching of treatment group subjects with similar subjects (matching a student in the study with a student in a similar grade, with similar test scores, and similar demographic characteristics; and likewise for all of the subjects in the treatment group, for instance).