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Experimental Research - PowerPoint PPT Presentation


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Experimental Research. Experimental Research. Take some action and observe its effects Extension of natural science to social science Best for limited and well defined concepts Useful for hypothesis testing - need theory Focus on determining causation, not just description .

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experimental research2
Experimental Research
  • Take some action and observe its effects
    • Extension of natural science to social science
    • Best for limited and well defined concepts
    • Useful for hypothesis testing - need theory
    • Focus on determining causation, not just description
components of experiment
Components of Experiment
  • Three components:
    • Independent and dependent variables
      • Effects of stimulus on some outcome variable
    • Pretesting and posttesting
      • Ability to assess change before and after manipulation
    • Experimental and control groups
      • Comparison group that does not get stimulus
experimental and control groups
Experimental and Control Groups
  • Must be as similar as possible.
  • Control group represents what the experimental group would have been like had it not been exposed to the experimental stimulus.
selecting subjects
Selecting Subjects
  • Probability sampling
  • Randomization
    • Most statistics used to analyze results assume randomization of subjects.
    • Randomization only makes sense if you have a reasonably large pool of subjects.
pre experimental designs
Pre-Experimental Designs
  • On-Shot Case Study
  • One Group Pretest-

Posttest Design

  • Static Group

Comparison

solomon four group design
Solomon Four-Group Design
  • Classic Design may sensitize subjects
  • More complex experimental designs
posttest only control group design
Posttest-only Control Group Design
  • Includes Groups 3 and 4 of the Solomon design.
  • With proper randomization, only these groups are needed to control the problems of internal invalidity and the interaction between testing and stimulus.
other design considerations
Other Design Considerations
  • Double blind - no experimenter bias
  • Subject selection - convenience or representative
    • Generalizability vs. explanatory power
    • Comparability of experimental and control groups
    • Probability sampling for representativeness
    • Randomization over matching for equivalence
threats to validity in experiments
Threats to Validity in Experiments
  • History - intervening event
  • Maturation - people change
  • Testing - respond to measures
  • Instrumentation - change measures
  • Regression - Regress to mean
  • Selection biases - incomparable groups
  • Experimental mortality - Drop out of study
  • Diffusion of treatment - contamination of control
  • Compensation - advantage control group
  • Compensatory rivalry - control group competes harder
  • Demoralization - control group may give up
  • + External Threats to Validity / Interactions with Stimulus
natural experiments
"Natural" Experiments
  • Important social scientific experiments occur outside controlled settings and in the course of normal social events.
  • Raise validity issues because researcher must take things as they occur.
time and survey design
Time and Survey Design
  • Extending logic of Experimentation to Surveys
    • Static designs:
      • Cross-sectional study
    • Longitudinal designs:
      • Trend studies
      • Cohort studies
      • Panel studies
experimental method
Experimental Method

Strengths:

  • Isolation of the experimental variable over time.
  • Experiments can be replicated several times using different groups of subjects.

Weaknesses:

  • Artificiality of laboratory setting.
  • Social processes that occur in a lab might not occur in a more natural social setting.