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

control factor

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

Simple example of a Correlational Design

Use of Correlational Design to Identify Unusual Cases

--More Complex Example-- Late 20th C Immigration and Internal Migration Patterns for U.S. Metro. Areas

Migration Components

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

TRUE EXPER QUASI-----CORRELATIONAL more < ARTIFICIALITY less result less EXTERNAL VALIDITY > more