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 :
Maturation (Emotional, Physical & Psychological)
One Group pretest-Post test design :
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:
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. •
(Quasi experimental group)
(Non equivalent control group)
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:
Quasi expérimental group
Non equivalent control group O1
Design lets us see whether the two groups scored similarly on the...
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