Download - Chapter 10 Designing Quantitative Studies

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Chapter 10

Designing Quantitative Studies


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.


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


Research Design Terminology in the Social Scientific and Medical Literature

Research Design Terminology in the Social Scientific and Medical Literature


Experiments or Randomized Controlled Trial (RCT) Properties

Experiments or Randomized Controlled Trial (RCT) Properties

1. Manipulation

2. Control

3. Randomization


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


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


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


Small Table of Random Digits Small Table of Random Digits


Example of Random Assignment Procedure

Example of Random Assignment Procedure


Breakdown of the Gender Composition of the Three Groups

Breakdown of the Gender Composition of the Three Groups


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


Experimental Designs Experimental Designs


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


Factorial DesignsFactorial Designs

• Two or more variables are manipulated simultaneously

• Test both main effects and interaction effects

• Randomized block design

• Crossover design


Example of a Factorial Design Example of a Factorial Design


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


Quasi-Experimental DesignsQuasi-Experimental Designs

• Time series design

• Nonequivalent control group before-after

design


Time Series DesignTime Series Design

O1 O2 O3 O4 X O5 O6 O7 O8


Other Quasi-Experimental DesignsOther Quasi-Experimental Designs

• Regression discontinuity design

• Quasi-experimental dose-response analyses

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


Nonexperimental (or Observational) Research

Nonexperimental (or Observational) Research

• Descriptive research

• Correlational studies


Designs of Correlational StudiesDesigns of Correlational Studies

• Retrospective (case-control) design

• Prospective (cohort) designs

• Natural experiments

• Path analytic studies


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


Descriptive StudiesDescriptive Studies

• Prevalence studies

• Incidence studies