When might a quasi-experimental design be chosen over an experimental design? What considerations must a researcher make when deciding which approach to take?

In quasi-experimental research, groups have already been assigned to a group. For example, when comparing eye color, gender or ethnicity among participants, these are predetermined factors. “A quasi-experimental design is one that looks a bit like an experimental design but lacks the key ingredient -- random assignment.” (Trochim, 2006, para 1) Researchers have no control over the groups as they are predetermined. Quasi-experimental research does allow the random assignment of people to groups; however, you can not randomly assignment treatments to the groups. . .

This article addresses: When might a quasi-experimental design be chosen over an experimental design? What considerations must a researcher make when deciding which approach to take? What are the threats to validity and reliability is this design trying to control for?