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

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



Experiments or randomized controlled trial rct properties
Experiments or Randomized Controlled Trial (RCT) Properties Medical Literature

  • Manipulation

  • Control

  • Randomization


Manipulation
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
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
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
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 designs1
Experimental Designs Medical Literature


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 designs
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 preexperimental designs
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


Quasi experimental designs
Quasi-Experimental Designs Design

  • Time series design

  • Nonequivalent control group before-after

    design


Time series design
Time Series Design Design

O1 O2 O3 O4 X O5 O6 O7 O8


Other quasi experimental designs
Other Quasi-Experimental Designs Design

  • 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 Design

  • Descriptive research

  • Correlational studies


Designs of correlational studies
Designs of Correlational Studies Design

  • Retrospective (case-control) design

  • Prospective (cohort) designs

  • Natural experiments

  • Path analytic studies


Continuum of designs for inferring causality
Continuum of Designs for Inferring Causality Design

Strongest

Weakest

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

correlational correlational


Descriptive studies
Descriptive Studies Design

  • Prevalence studies

  • Incidence studies


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