Chapter 10 designing quantitative studies
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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 10 Designing Quantitative Studies

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Chapter 10 designing quantitative studies

Chapter 10Designing Quantitative Studies


The counterfactual method

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

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


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

  • Manipulation

  • Control

  • Randomization


Manipulation

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

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

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 designs

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


Experimental designs1

Experimental Designs


Symbolic representation of a pretest posttest experimental design

Symbolic Representation of a Pretest-Posttest Experimental Design

RO1XO2

RO1O2

R = Randomization

O = An observation or measurement

X = An intervention


Factorial designs

Factorial 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 designs

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

Quasi-Experimental Designs

  • Time series design

  • Nonequivalent control group before-after

    design


Time series design

Time Series Design

O1O2O3O4X O5O6O7O8


Other quasi experimental designs

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

Nonexperimental (or Observational) Research

  • Descriptive research

  • Correlational studies


Designs of correlational studies

Designs 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-experimentPre-experiment Path analyticProspective Retrospective Descriptive

correlational correlational


Descriptive studies

Descriptive Studies

  • Prevalence studies

  • Incidence studies


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