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REAL WORLD RESEARCH SECOND EDITION

Threats to internal validity. HistoryTestingInstrumentationRegressionMortalityMaturation. continued.... SelectionSelection by maturation interactionAmbiguity about causal directionDiffusion of treatmentsCompensatory equalization of treatmentsCompensatory rivalry(after Cook and Campbell,

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REAL WORLD RESEARCH SECOND EDITION

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    1. REAL WORLD RESEARCH SECOND EDITION Chapter 5: Fixed Designs

    2. Threats to internal validity History Testing Instrumentation Regression Mortality Maturation Box 5.1 p. 105Box 5.1 p. 105

    3. Selection Selection by maturation interaction Ambiguity about causal direction Diffusion of treatments Compensatory equalization of treatments Compensatory rivalry (after Cook and Campbell, 1979) Threats to internal validity Box 5.1 p. 105Box 5.1 p. 105

    4. Threats to generalizability (external validity) Selection Setting History Construct effects (after LeCompte and Goetz, 1982) Box 5.2 p. 107Box 5.2 p. 107

    5. Problems in carrying out field experiments Random assignment – practical and ethical problems Questionable validity Ethical issues Lack of control Box 5.3 p. 113Box 5.3 p. 113

    6. Advantages of field experiments Compared with lab experiments: Generalizability to real world easier Validity improved Easier to get participants Box 5.4 p. 115Box 5.4 p. 115

    7. Explanations of inconclusive results of many ‘social’ RCTs The intervention is ineffective Design or implementation of the RCT is faulty RCT methodology is inappropriate p. 118p. 118

    8. Some ‘true’ experimental designs Two group designs Post-test-only randomized controlled trial (RCT) Post-test-only two treatment comparison Pre-test post-test RCT Pre-test post-test two treatment comparison Three (or more) group simple designs As above but more groups. Box 5.5 p. 124Box 5.5 p. 124

    9. Some ‘true’ experimental designs Box 5.5 p. 124Box 5.5 p. 124

    10. Situations where randomized experiments might be considered When lotteries are expected When demand outstrips supply When innovations have to be introduced gradually When experimental units are isolated from each other When it is agreed that change should take place but there is no consensus about solutions When persons express no preference among alternatives When you are involved in setting up an organization (after Cook and Campbell, 1979) Box 5.13 p. 135Box 5.13 p. 135

    11. Some quasi-experimental designs Pre-experimental designs (AVOID – difficult to interpret results) Single-group post-test only Post-test only non-equivalent groups Pre-test post-test single group design Pre-test post-test non-equivalent group designs Interrupted time-series designs Regression-discontinuity designs

    12. Some single case designs Note: These designs call for a series of measures on the dependent variable(s) A-B designs A-B-A designs A-B-A-B designs Multiple base-line designs across settings across behaviours across participants

    13. Some non-experimental fixed designs Note: Same general approach as in experimental designs but without active manipulation of variables Relational designs (correlational studies) Cross-sectional designs Prediction studies Comparative designs Longitudinal designs Box 5.20 p. 148Box 5.20 p. 148

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