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Research Design

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Research design is the scheme that guides the ... It is a logical model of proof that allows the making of valid causal inferences. ... Ex Post Facto Experiment ... – PowerPoint PPT presentation

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Title: Research Design


1
Research Design
  • Session 12

2
Research Design
  • Well, lets define it . . .
  • Research design is the scheme that guides the
    process of collecting, analyzing, and
    interpreting data. It is a logical model of
    proof that allows the making of valid causal
    inferences.
  • Less formally stated . . . it is the plan for
    your research that best establishes causal
    relationships, and provides the best way to
    answer the questions that you have.

3
Elements of Research Design
  • Which . . . ?
  • variables which ones best measure the phenomena
    that interest me?
  • analytical strategy is this a question for an
    experimental design, a statistical analysis?
  • theory do I think there is reciprocal causality
    here, multi-stage causality, causality over time
    . . ?
  • hypotheses can I actually test the questions I
    have raised here with the design, variables, etc.
    that I have chosen?

4
Experimental Research Designs
  • Experimental Design includes
  • Experimental group
  • Control group
  • Stimulus or treatment (terms can be used
    interchangeably)
  • Test

5
Variations in Experimental Design
  • Classic Experimental Design
  • Solomon Two-Control-Group Design
  • Solomon Three-Control-Group Design
  • Assigning Cases to Groups
  • Precision Matching
  • Frequency Distribution Control
  • Randomization

6
Field Experiments and Nonexperimental Design
  • Field Experiments
  • Real world setting
  • Careful selection of subjects and random
    assignment of subjects to the test and control
    groups to maximize control over background
    characteristics that might influence results
  • Monitoring of subjects circumstances throughout
    the experiment to prevent alternative causality

7
  • Nonexperimental Designs
  • Researcher cannot control the assignment of
    subjects to experimental groups nor the
    occurrence of the independent variable
  • Cannot obtain pretest scores on the dependent
    variable
  • May use after-only design a single observation
    of the presumed causal event

8
Quasi-Experimental Designs
  • Quasi-Experimental Designs
  • Researcher does not control exposure to the
    independent variable or accompanying conditions
  • Researcher creates conditions of an experiment
    though collection of additional data

9
Quasi, Continued
  • Ex Post Facto Experiment
  • Researcher makes a single observation and
    collects data about the independent and dependent
    variables
  • Time Series
  • Researcher makes several observations both before
    and after the introduction of some causal
    phenomenon and compares values on the dependent
    variable before and after
  • Researcher observes the trend line

10
Quasi, Continued
  • Controlled Time Series
  • Researcher gathers data on a group similar to the
    original group except in exposure to the
    treatment to use as a control group

11
V is for . . . No, Not Victory
  • Internal Validity the degree to which the
    design provides a sound logical basis for
    inferring that the independent variable does or
    does not cause a change in the dependent variable
  • External Validity the generalizability of our
    results

12
Factors that Threaten Validity
  • Internal History, Maturation, Instability,
    Testing, Instrumentation, Regression Artifacts,
    Selection, Experimental Mortality
  • External Testing, Treatment, Irrelevant
    Response, Replicability
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