Chapter 10 Designing Quantitative Studies
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Transcript of Chapter 10 Designing Quantitative Studies
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Chapter 10
Designing Quantitative Studies
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
The Counterfactual MethodThe 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.
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
CausalityCausality
• 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
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Research Design Terminology in the Social Scientific and Medical Literature
Research Design Terminology in the Social Scientific and Medical Literature
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Experiments or Randomized Controlled Trial (RCT) Properties
Experiments or Randomized Controlled Trial (RCT) Properties
1. Manipulation
2. Control
3. Randomization
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
ManipulationManipulation
• 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
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Control GroupControl Group
• Researchers can expose the control group to various conditions:
– no treatment
– alternative treatment
– placebo
– standard treatment
– different doses of the treatment
– wait-list
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Randomization (Random Assignment, Random Allocation)
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
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Small Table of Random Digits Small Table of Random Digits
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Example of Random Assignment Procedure
Example of Random Assignment Procedure
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Breakdown of the Gender Composition of the Three Groups
Breakdown of the Gender Composition of the Three Groups
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Experimental DesignsExperimental Designs
•After-only (posttest-only) design
•Before-after (pretest-posttest) design
•Solomon four-group design
•Factorial design
•Randomized block design
•Crossover (repeated measures) design
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Experimental Designs Experimental Designs
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Symbolic Representation of a Pretest-Posttest Experimental Design
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
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Factorial DesignsFactorial Designs
• Two or more variables are manipulated simultaneously
• Test both main effects and interaction effects
• Randomized block design
• Crossover design
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Example of a Factorial Design Example of a Factorial Design
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Quasi-Experimental and Preexperimental DesignsQuasi-Experimental and Preexperimental Designs
Nonequivalent control group pretest-posttest design (quasi-experimental)
O1 X O2
O1 O2
Nonequivalent control group posttest-only design (preexperimental)
X OO
One group pretest-posttest design (preexperimental)O1 X O2
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Quasi-Experimental DesignsQuasi-Experimental Designs
• Time series design
• Nonequivalent control group before-after
design
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Time Series DesignTime Series Design
O1 O2 O3 O4 X O5 O6 O7 O8
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Other Quasi-Experimental DesignsOther Quasi-Experimental Designs
• Regression discontinuity design
• Quasi-experimental dose-response analyses
• Quasi-experimental (nonrandomized) arms of a PRPP randomization design
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Nonexperimental (or Observational) Research
Nonexperimental (or Observational) Research
• Descriptive research
• Correlational studies
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Designs of Correlational StudiesDesigns of Correlational Studies
• Retrospective (case-control) design
• Prospective (cohort) designs
• Natural experiments
• Path analytic studies
Copyright © 2008 Wolters Kluwer Health | Lippincott Williams & Wilkins
Continuum of Designs for Inferring Causality
Continuum of Designs for Inferring Causality
Strongest Weakest
True experiment Quasi-experiment Pre-experiment Path analytic Prospective Retrospective Descriptivecorrelational correlational
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Descriptive StudiesDescriptive Studies
• Prevalence studies
• Incidence studies