4-19-11 - 4-19-11 Quasi-Experimental Designs - Virtually...

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Unformatted text preview: 4-19-11 Quasi-Experimental Designs - Virtually identical to true experimental designs with the exception of random assignment - An IV is manipulated and a DV measured - Cannot make causal inferences as groups may not be equal - Necessary when random assignment not possible - Some categorize ex post facto and quasi together o Ex post facto = cant control or manipulate pre-existing conditions so cant randomly assign Ss to groups; In quasi we do have control over IV o Step closer than ex post facto to true experiment; exert control over IV and its administration (Boys/girls need English help, IV is workshop) - When to use this design o If we study Ss from certain groups (based on sex, age, previous life experiences, personality characteristics) o Evaluate an ongoing program or intervention Program began before you wanted to start evaluating it Studies of social conditions • Poverty, race, unemployment or other social factors Random assignment not possible because of expense, time, or monitoring difficulty - Nonequivalent group design involves two or more groups that are not randomly assigned which is why called nonequivalent o A comparison group is compared to one or more treatment groups o Important to select comparison group as similar as possible o Text example – we wanted to look at teen mothers, want a good comparison group so we are going to look at their isters who did not become pregnant until later in life Similar background factors - Interrupted time-series design o Involves a single group of participants o Includes repeated pretreatment measures, an applied treatment, and repeated post treatment measures o History main threat to internal validity REVIEW INTERNAL VALIDITY ...
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This note was uploaded on 04/05/2012 for the course PSY 3213 taught by Professor Staff during the Spring '11 term at FSU.

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