Quasi experiments are a type of non-experimental research where subjects are not randomly assigned to conditions but are instead selected based on pre-existing characteristics. While they lack random assignment, quasi experiments attempt to mimic experimental designs and evaluate causal relationships. Key differences from true experiments include an inability to fully control variables and reduced internal validity due to lack of randomization. However, quasi experiments may have higher external validity if the research setting more closely matches the real world. Examples of quasi experimental designs include nonequivalent control group designs and mixed factorial designs with non-manipulated variables.