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Experimental Research Designs

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Title: Experimental Research Designs


1
Experimental Research Designs
  • Research Process and Design
  • Spring 2006
  • Class 6

2
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

3
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

4
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

5
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

6
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

7
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

8
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

9
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

10
Single-Subject Designs
  • AB designs
  • ABA or ABAB designs
  • Multiple baseline designs
  • Multiple baselines across behaviors
  • Multiple baselines across situations
  • Multiple baselines across individuals

11
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?

12
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?

13
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?

14
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)
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