Experimental Research Designs

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Experimental Research Designs

• Research Process and Design
• Spring 2006
• Class 6

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Todays objectives

• To answer any questions you have
• To understand the characteristics, strengths and
  weaknesses of experimental research designs
• To explore the various experimental designs
• To apply knowledge in an activity and to your
  group project

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Experimental Research

• Purpose
• make causal inferences about the relationship
  between the independent and dependent variables
• rule out rival hypotheses
• Types
• Pre-experimental
• True (randomized) experimental
• Quasi-experimental
• Single-subject

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Characteristics of Experimental Research

• Statistical equivalence of subject in different
  groups (usually by random assignment)
• Comparison of 2 or more groups
• Manipulation of at least 1 IV
• Measurement of DVs
• Inferential statistics
• Maximum control of extraneous variables

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Experimental ResearchStrengths and Limitations

• Strengths
• The only designs capable of examining causal
  relationships
• High degree of control of extraneous variables
• Direct manipulation of an independent variable
• Weaknesses
• High levels of control needed for assuring
  internal validity mean very restrictive
  manipulated conditions which in turn imply low
  external validity
• High levels of external validity mean little
  control and thus low internal validity
• Not possible in many situations

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Notation

• R Random assignment
• O Observation
• X Treatment condition (may have subscripts to
  denote different treatments)
• A, B, C, D, E, F Groups of subjects

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Pre-Experimental

• One group posttest only
• Internal history, maturation, selection,
  mortality
• External interaction of selection and x
• One group pretest posttest
• Internal history, maturation, selection,
  mortality
• External interaction of selection and x
  interaction of testing and x
• Time-Series
• Single group interrupted time series
• Internal history, maturation, selection,
  mortality
• External interaction of selection and x
  interaction of testing and x

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Quasi-Experimental

• Non-equivalent groups posttest only
• Non-equivalent groups posttest only control
• Non-equivalent groups posttest only comparison
• Internal history, maturation, selection,
  mortality
• External interaction of selection and x
• Non-equivalent groups pretest-posttest
• Non-equivalent groups pretest-posttest control
  
• Non-equivalent groups pretest-posttest comparison
  
• Non-equivalent groups pretest-posttest
  control/comparison
• Internal history, maturation, selection,
  mortality, pre-test
• External interaction of selection and x

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True Experimental

• Pretest-posttest control group
• Pretest-posttest comparison group
• Pretest-posttest control/comparison group
• Posttest only control group
• Posttest only comparison group
• Posttest only control/comparison group
• Solomon four-group design

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Single-Subject Designs

• AB designs
• ABA or ABAB designs
• Multiple baseline designs
• Multiple baselines across behaviors
• Multiple baselines across situations
• Multiple baselines across individuals

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Discussion questions (Steele and Aronson)

• What constructs are they studying?
• How are they measuring the constructs?
• Who are they studying?
• What design have they employed?
• What did they find?
• How have they controlled for extraneous/confoundin
  g variables?
• What are the threats to internal and external
  validity
• How might they have improved the study?

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Activity 1

• Divide into groups of three
• Each group will be assigned a design
• Pre-experimental
• Quasi-experimental
• True experimental
• Re-design Antonio et al. by applying your
  assigned design. Be specific.
• What threats to internal and external validity
  should be considered?

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Activity 2

• Design a study using 2 of the research designs
  described in todays class.
• What are the implications of each design?
• What are the pros and cons of each design?

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For next week

• Methods section and research design continued
• Readings
• Creswell Ch. 9
• Gall, Borg, Gall Ch. 13
• Reminder Outline of literature review due in 2
  weeks (one per group)