A. True Experiment Purpose??? Key to achieving???.
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Transcript of A. True Experiment Purpose??? Key to achieving???.
B. Quasi-experiment
Is a treatment but the researcher often does not introduce the intervention or treatment.
e.g. ---Hazards research
The assignment of subjects to treatment conditions is not random
e.g.---intact classrooms
X
Internal Validity Threats in Quasi-Experimental
Designs
• Group threat of Nonequivalence
• example of Head Start programs
-----Subtype-----Single Group Interrupted Time
Series design
X
•Is there an intervention effect???
•Problem---Time threats to internal validity
Time--------------------------->
Examples of single group interrupted time series designs
Single district studies of impacts of implementation of school desegregation plans on:
–student achievement
–white enrollment declines
Strategy for handling time threats in interrupted time series
Multiple group interrupted time series designs
X
C. Correlational or EX POST FACTO Designs
•Researcher has no control over either assignment or treatment
•Starts with effect and works backwards in time to identify causes.
Most common design type in quantitative social research
--More Complex Example--
Late 20th C Immigration and Internal Migration Patterns for
U.S. Metro. Areas
1985-1990 Migration Components
Metro area Immigration Internalmigration
Los Angeles 899,007 -174,673New York 756,034 -1,065,580San Francisco 293,306 -103,498Miami 210,609 45,287Chicago 179,524 -293,185
TRUE EXPER. ---- QUASI -----CORRELATIONAL
more <------------CONTROL----------------------less
result
more <--------INTERNAL VALIDITY-------- less
The EXTERNAL VALIDITY issue
(generalizability)
Threats to generalizability:
•nonrepresentative subjects
•put in artificial settings
•submitted to artificial trreatments