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 Ð"©quivalent groups prÐ"©-test- post test design:

o Quasi expÐ"©rimental group O1 X O2

o Non equivalent control group O1 -- O2

 Design lets us see whether the two groups scored similarly on the dependent variable.

 However

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