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EXPERIMENTAL RESEARCH

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... at Madigan Army Medical Center examined effectiveness of duct tape on warts. ... Warts were successfully removed in 60 percent (15 of 25) of the patients in the ... – PowerPoint PPT presentation

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Title: EXPERIMENTAL RESEARCH


1
EXPERIMENTAL RESEARCH

2
Experiments
  • Allow demonstration of causality
  • A causes B
  • Relatively small sample sizes needed
  • Minimum of 20 per experimental cell

3
VARIABLES Independent and Dependent
  • CAUSE
  • Independent variable
  • OUTCOME
  • Dependent variable

CAUSE
OUTCOME
4
Requirements for Causality (X Y)
  • Temporal ordering of variables
  • Evidence of association
  • Control of other causal factors

5
Experiments
  • Manipulate variable of interest
  • Independent variable IV
  • (Variable we can control)
  • Hold all else constant
  • Extraneous variables
  • Measure outcome
  • Dependent variable DV
  • (Variable we cannot directly control)

6
Duct tape and warts
  • Researchers at Madigan Army Medical Center
    examined effectiveness of duct tape on warts.
  • The 51 patients between 3 and 22 were randomly
    assigned to receive either cryotherapy or duct
    tape. Patients in the cryotherapy group received
    a standard 10 second application of liquid
    nitrogen, repeated every two to three weeks. In
    the other group, a small piece of duct tape was
    placed on the patients' warts and patients were
    told to keep the tape on for six days. At the end
    of six days, they removed the tape, soaked the
    area in water, and used an emery board or pumice
    stone to rub the dead skin off.
  • Warts were successfully removed in 60 percent (15
    of 25) of the patients in the cryotherapy group
    versus 85 percent (22 of 26) of the patients in
    the duct tape group. The duct tape group reported
    fewer side effects than cryotherapy group who
    reported pain and burning at the site.
  • Overall, the researchers found duct tape to be
    more effective, less painful, and less expensive
    than freezing.

7
Experimental Design
  • Assignment to condition
  • Randomly assign subjects to condition OR
  • Match subjects on variable of interest
  • Manipulation
  • Experimental group gets it
  • Control group does not get it
  • Measurement of DV
  • Pretest
  • Posttest

8
Control of Extraneous Variables
  • DESIGN
  • Eliminate Extraneous Variables
  • Hold Conditions Constant
  • Counterbalance
  • SUBJECTS
  • Match Subjects
  • Randomization

9
True Experimental Designs
  • Random assignment to condition
  • Many types, including
  • pretest posttest control group
  • posttest only control group
  • completely randomized
  • randomized block
  • Solomon Four
  • Latin Square
  • Factorial design

10
True Experimental Designs
  • Pretest posttest control group design
  • Experimental Group R O1 X O2
  • Control Group R O3 O4
  • Posttest only control group design
  • Experimental Group R X O1
  • Control Group R O2

11
Solomon Four
Experimental Group 1 R O1 X O2 Control
Group 1 R O3 O4 Experimental Group
2 R X O5 Control Group 2 R
X O6
Combination of pretest-posttest control group and
posttest only control group designs.
12
Factorial Design
  • Design that investigates the effect of two or
    more independent variables on a dependent
    variable
  • Allows testing of interactions

13
Effects
  • Main effect
  • Additive or linear effects on the dependent
    variable.
  • Interaction effect
  • Non-additive influences by a combination of two
    or more independent variables.
  • Effect of A depends on B, too,

14
2 x 2 Factorial Design
Ad A Ad B
Men Women
65 65
Main Effects of Gender
gt
70 60
gt
Main Effects of Ad
15
Interaction Between Gender and Advertising Copy

16
Key Points
  • Experimental research is the only way to
    demonstrate causation.
  • Experimental research is inherently
    reductionistic.
  • Complex designs allow the comparison of several
    factors simultaneously, including interactions.

17
The End
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