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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

Chapter 10 Designing Quantitative Studies

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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

### Experiments or Randomized Controlled Trial (RCT) Properties

• Manipulation

• Control

• Randomization

### 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

### Symbolic Representation of a Pretest-Posttest Experimental Design

RO1XO2

RO1O2

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)O1XO2O1O2Nonequivalent control group posttest-only design (preexperimental)XOOOne group pretest-posttest design (preexperimental)O1XO2

### Quasi-Experimental Designs

• Time series design

• Nonequivalent control group before-after

design

### Time Series Design

O1O2O3O4X O5O6O7O8

### 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-experimentPre-experiment Path analyticProspective Retrospective Descriptive

correlational correlational

### Descriptive Studies

• Prevalence studies

• Incidence studies