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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 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.

• 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 Medical Literature

• Manipulation

• Control

• Randomization

Manipulation Medical Literature

• 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 Medical Literature

• 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) Medical Literature

• 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 Medical Literature

• After-only (posttest-only) design

• Before-after (pretest-posttest) design

• Solomon four-group design

• Factorial design

• Randomized block design

• Crossover (repeated measures) design

Experimental Designs Medical Literature

R O1 X O2

R O1 O2

R = Randomization

O = An observation or measurement

X = An intervention

Factorial Designs Design

• Two or more variables are manipulated simultaneously

• Test both main effects and interaction effects

• Randomized block design

• Crossover design

Quasi-Experimental and DesignPreexperimental 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

• Time series design

• Nonequivalent control group before-after

design

Time Series Design Design

O1 O2 O3 O4 X O5 O6 O7 O8

• Regression discontinuity design

• Quasi-experimental dose-response analyses

• Quasi-experimental (nonrandomized) arms of a PRPP randomization design

• Descriptive research

• Correlational studies

• Retrospective (case-control) design

• Prospective (cohort) designs

• Natural experiments

• Path analytic studies

Strongest

Weakest

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

correlational correlational

Descriptive Studies Design

• Prevalence studies

• Incidence studies