1. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 10 Designing Quantitative Studies

2. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 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. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 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. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Research Design Terminology in the Social Scientific and Medical Literature

5. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Experiments or Randomized Controlled Trial (RCT) Properties 1.Manipulation 2.Control 3.Randomization

6. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 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. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 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. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 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. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Small Table of Random Digits

10. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Example of Random Assignment Procedure

11. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Breakdown of the Gender Composition of the Three Groups

12. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins 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. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Experimental Designs

14. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Symbolic Representation of a Pretest- Posttest Experimental Design RO 1 XO 2 RO 1 O 2 R = Randomization O = An observation or measurement X = An intervention

15. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Factorial Designs Two or more variables are manipulated simultaneously Test both main effects and interaction effects Randomized block design Crossover design

16. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Example of a Factorial Design

17. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Quasi-Experimental and Preexperimental Designs Nonequivalent control group pretest-posttest design (quasi- experimental) O 1 XO 2 O 1 O 2 Nonequivalent control group posttest-only design (preexperimental) XO O One group pretest-posttest design (preexperimental) O 1 XO 2

18. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Quasi-Experimental Designs Time series design Nonequivalent control group before-after design

19. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Time Series Design O 1 O 2 O 3 O 4 X O 5 O 6 O 7 O 8

20. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Other Quasi-Experimental Designs Regression discontinuity design Quasi-experimental dose-response analyses Quasi-experimental (nonrandomized) arms of a PRPP randomization design

21. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Nonexperimental (or Observational) Research Descriptive research Correlational studies

22. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Designs of Correlational Studies Retrospective (case-control) design Prospective (cohort) designs Natural experiments Path analytic studies

23. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Continuum of Designs for Inferring Causality Strongest Weakest True experiment Quasi-experimentPre-experiment Path analyticProspective Retrospective Descriptive correlational

24. Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins Descriptive Studies Prevalence studies Incidence studies