Quasi experiment

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Quasi experiment

By | June 2008
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-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. oQuasi 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 :
oHistory
oMaturation (Emotional, Physical & Psychological)
oMortality
oTesting

-One Group pretest-Post test design :
oPoor research strategy because it fails to eliminate most threats to internal validity. oHistory, 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:
oOne 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. •XO(Quasi experimental group)

---O(Non equivalent control group)
oMany 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:
oQuasi expérimental groupO1XO2
oNon equivalent control group O1--O2
Design lets us see whether the two groups scored similarly on the...