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Chapter Ten: Experimental Research considered to be the "gold…

- - - - high in internal validity; low external validity because lab setting may not reflect the real world
    - - high in both internal and external validity
  - - - many of the measurement instruments used in experimental research are not tested for reliability and validity, and are incomparable across studies
        
        often experimental research uses inappropriate research designs
        
        Findings from such studies tend to lack internal validity and are highly suspect
        
        treatments used in experimental research may be diverse, incomparable, and inconsistent across studies, and sometimes inappropriate for the subject population
        
        introduces new threats to internal validity, generates findings that are non-interpretable and meaningless, and makes integration of findings across studies impossible
        
        results generated using such instruments are also incomparable
      - hypotheses being tested tend to be ad hoc, possibly illogical, and meaningless
- - - - non-equivalent groups design:
        quasi-equivalent version of pretest-posttest control group design
      - non-equivalent switched replication design:
        quasi-experimental version of switched replication design
    - - Regression discontinuity (RD) design:
        subjects are assigned to the treatment or control group based on a cut-off score on a preprogram measure
      - Proxy pretest design:
        very similar to the standard NEGD (pretest-posttest) design, but the pretest score is collected after the treatment is administered
      - Separate pretest-posttest samples design:
        useful if it is not possible to collect pretest and posttest data from the same subjects for some reason
      - Non-equivalent dependent variable (NEDV) design:
        single-group pre-post quasi-experimental design with two outcome measures, where one measure is theoretically expected to be influenced by the treatment and the other measure is not
- - - - Random Selection and Assignment:
        the process of randomly drawing a sample from a population or a sampling frame and randomly assigning subjects to experimental or control groups
        
        Random selection is related to sampling, and is related to the external validity
        
        random assignment is related to design, and is most related to internal validity
        
        Threats to Internal Validity
        
        History Threat:
        the possibility that observed effects are caused by extraneous or historical events rather than by the experimental treatment
        
        Maturation Threat:
        the possibility that observed effects are caused by natural maturation of subjects
        
        Testing Threat:
        threat in pre-post designs where subjects’ posttest responses are conditioned by their pretest responses
        
        Instrumentation Threat:
        the possibility that the difference between pretest and posttest scores is due to changes in the test
        
        Mortality Threat:
        the possibility that subjects may be dropping out of the study at differential rates between the treatment and control groups due to a systematic reason
        
        Regression Threat:
        statistical tendency of a group’s overall performance to regress toward the mean during a posttest rather than in the anticipated direction
    - - pretest measures:
        measurements conducted before the treatment
      - posttest measures:
        measurements conducted after the treatment