Quasi Experiment

- Quasi Experimental Design: If the researcher lacks control over the assignment of participants to conditions and does not manipulate the causal variable of interest, the design is quasi experimental. o Quasi Experiments do not have internal validity because participants are not randomly assigned to conditions and the researcher may have no control over the independent variable.

- Basic Confounds in Quasi Experimental Design are : o History o Maturation (Emotional, Physical & Psychological) o Mortality o Testing

- One Group pretest-Post test design : o Poor research strategy because it fails to eliminate most threats to internal validity. o History, Maturation, Mortality and testing are some examples of the confounds in this experiment
 Ex: Drug use between O1 and O2:
• Could have been because students may have matured from the pre test to post test (Maturation effects)
• Could have been because one of the popular rock artist died of drug overdose which led to decrease in drug use (Mortality effects)
• Events other that the program may have occurred between O1 and O2 (History effects)
• O1 may have started thinking about drugs, resulting in lower use ( testing effect)

- Non equivalent groups Posttest-only design: o One option is to measure both groups after one of them has received the quasi experimental treatment.
 Ex: assessing drug use among students at the school who used the anti-drug use program to students from another school who didn’t use anti-drug use program.
• X O (Quasi experimental group)
• --- O (Non equivalent control group) o Many weaknesses:
 We don’t know if the groups were equivalent before participants received the quasi independent variable
 Non equivalent post group is very weak in terms of internal validity.

- Non équivalent groups pré-test- post test design: o Quasi expérimental group O1 X O2 o Non equivalent control group O1 -- O2
 Design lets us see whether the two groups scored similarly on the