Quasi-experimental design is a research method that evaluates the effect of an intervention or treatment without random assignment of participants. Instead of randomly assigning subjects to control and experimental groups, researchers use existing groups or conditions, which can lead to potential biases. This design is often used in social sciences and education where randomization may not be feasible. Despite its limitations, quasi-experimental design allows researchers to draw conclusions about causal relationships. By comparing outcomes between groups that have received different treatments or interventions, researchers can identify patterns and effects, making it a valuable tool in fields like psychology and public health.