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Chapter 10 Designing Quantitative Studies

Chapter 10 Designing Quantitative Studies. The Counterfactual Method. The counterfactual is what would have happened to the same people simultaneously exposed and not exposed to the causal factor. Effect represents the difference between the two. Causality. The Counterfactual Method

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Chapter 10 Designing Quantitative Studies

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  1. Chapter 10Designing Quantitative Studies

  2. The Counterfactual Method • The counterfactual is what would have happened to the same people simultaneously exposed and not exposed to the causal factor. • Effect represents the difference between the two.

  3. Causality • The Counterfactual Method • Criteria for Causality—Lazarsfeld (1955) 1. Temporal 2. Empirical relationship 3. Relationship cannot be explained as being caused by a third variable

  4. Research Design Terminology in the Social Scientific and Medical Literature

  5. Experiments or Randomized Controlled Trial (RCT) Properties • Manipulation • Control • Randomization

  6. Manipulation • Doing something to study participants • Experimenter manipulates the independent variable by administering a treatment (intervention) to some subjects and withholding it from others, or by administering some other treatment

  7. Control Group • Researchers can expose the control group to various conditions: – no treatment – alternative treatment – placebo – standard treatment – different doses of the treatment – wait-list

  8. Randomization (Random Assignment, Random Allocation) • Involves placing subjects into treatment conditions at random • Approximates the ideal—but impossible—counterfactual of having the same people in multiple treatment groups simultaneously • Basic randomization

  9. Small Table of Random Digits

  10. Example of Random Assignment Procedure

  11. Breakdown of the Gender Composition of the Three Groups

  12. Experimental Designs • After-only (posttest-only) design • Before-after (pretest-posttest) design • Solomon four-group design • Factorial design • Randomized block design • Crossover (repeated measures) design

  13. Experimental Designs

  14. Symbolic Representation of a Pretest-Posttest Experimental Design R O1 X O2 R O1 O2 R = Randomization O = An observation or measurement X = An intervention

  15. Factorial Designs • Two or more variables are manipulated simultaneously • Test both main effects and interaction effects • Randomized block design • Crossover design

  16. Example of a Factorial Design

  17. Quasi-Experimental and Preexperimental Designs Nonequivalent control group pretest-posttest design (quasi-experimental)O1 X O2 O1 O2Nonequivalent control group posttest-only design (preexperimental) X O OOne group pretest-posttest design (preexperimental)O1 X O2

  18. Quasi-Experimental Designs • Time series design • Nonequivalent control group before-after design

  19. Time Series Design O1 O2 O3 O4 X O5 O6 O7 O8

  20. Other Quasi-Experimental Designs • Regression discontinuity design • Quasi-experimental dose-response analyses • Quasi-experimental (nonrandomized) arms of a PRPP randomization design

  21. Nonexperimental (or Observational) Research • Descriptive research • Correlational studies

  22. Designs of Correlational Studies • Retrospective (case-control) design • Prospective (cohort) designs • Natural experiments • Path analytic studies

  23. Continuum of Designs for Inferring Causality Strongest Weakest True experiment Quasi-experiment Pre-experiment Path analytic Prospective Retrospective Descriptive correlational correlational

  24. Descriptive Studies • Prevalence studies • Incidence studies

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