Differentiate between quasi and experimental methods.

In a true experiment, participants are randomly assigned to either the treatment or the control group, whereas they are not assigned randomly in a quasi-experiment. ... Thus, the researcher must try to statistically control for as many of these differences as possible. Quasi-experimental research involves the manipulation of an independent variable without the random assignment of participants to conditions or orders of conditions. Among the important types are nonequivalent groups designs, pretest-posttest, and interrupted time-series designs. In a true experiment, each participant who volunteered would have an equal chance of being assigned to any of the three groups. Quasi-experiments are employed when the researcher is interested in independent variables that cannot be randomly assigned.