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 Maturation (Emotional, Physical & Psychological)
- 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... [continues]
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