Chapter 10 Designing Quantitative Studies

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# Chapter 10 Designing Quantitative Studies - PowerPoint PPT Presentation

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 10Designing 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
• Criteria for Causality—Lazarsfeld (1955)

1. Temporal

2. Empirical relationship

3. Relationship cannot be explained as being caused by a third variable

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
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

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
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

R O1 X O2

R O1 O2

R = Randomization

O = An observation or measurement

X = An intervention

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

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

design

Time Series Design

O1 O2 O3 O4 X O5 O6 O7 O8

Other Quasi-Experimental Designs
• Regression discontinuity design
• Quasi-experimental dose-response analyses
• Quasi-experimental (nonrandomized) arms of a PRPP randomization design
Nonexperimental (or Observational) Research
• Descriptive research
• Correlational studies
Designs of Correlational Studies
• Retrospective (case-control) design
• Prospective (cohort) designs
• Natural experiments
• Path analytic studies
Continuum of Designs for Inferring Causality

Strongest

Weakest

True experiment Quasi-experiment Pre-experiment Path analytic Prospective Retrospective Descriptive

correlational correlational

Descriptive Studies
• Prevalence studies
• Incidence studies