Conducting Experiments

1
Conducting Experiments

• Psych 7
• February 15th

2
Announcements

• Midterm grades will be posted by Tuesday (this is
  my goal)
• Mook reading can be found on online reserve (use
  same password)

3
Outline

• Brief Review of Experimental Research
• Causation
• Manipulation Measurement
• Control Extraneous Variables
• Teasing out Effects Basic Experiments
• Before-after (prettest-posttest) design
• Posttest only design
• The Solomon design
• Artifacts, Experimenter Expectancy, and their
  Control
• Experiments Realism

4
Brief Review of Experimental Research

• Elements of a true experiment
• Establish the existence of a cause-effect
  relationship between two variables
• Manipulation
• Must rule out alternative explanations
• Control

5
Causation

• 3 Criteria of Causation
• Temporal precedence
• Cause before effect
• Covariation
• Cause present, effect present
• Cause absent, effect absent
• Alternate explanations
• Only cause gt effect

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Causation and the 3rd Variable Problem

• Its a Wonderful Experiment
• Experiments show us exactly how the
• world changes when you change only
• one thing
• If you want to know how whether one
• thing alone affects something else, you
• must hold everything else but that one
• thing constant
• http//www.angryalien.com/1204/wonderful_lifebuns.
  asp

7
Causation and the 3rd Variable Problem, cont.

• Freedman et al. (1974)
• Examined trends in family planning and birth
  control
• Results showed a strong positive relationship
  between television watching and use of birth
  control
• Do you accept this as a cause effect
  relationship?

8
Causation and the Directionality Problem

• Researchers may establish a relationship between
  2 variables
• Which is the cause and which is the effect?
• Example (Eagley Steffen, 1984)
• Relation between gender roles and gender
  stereotypes

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Manipulation and Measurement

• Manipulation
• Purpose

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Manipulation and Measurement, cont.

• Example
• Relation between insomnia and depression
• How can we determine the causal relationship?

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Manipulation and Measurement, cont.

• Manipulation typically involves creating 2
  treatment conditions
• Examines the relation between the IV and the DV
• Any other variables that exist in an experiment
  are called

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Control Extraneous Variables

• Must eliminate all confounding variables
• Characteristics of Confounding Variables

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Dealing with Extraneous Variables

• Control by Holding Constant
• e.g., test Ps in same room, at same time of day,
  but same researcher, etc.
• Control by Matching
• (e.g., same mean age or IQ per cond.)
• Control by Randomization

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Comparing Methods of Control
15
Advantages and Disadvantages of Control Methods

• Holding Constant and Matching
• Useful when one or two variables are identified
  as potential confounds
• Randomization

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Basic Experiments

• Posttest-Only Design

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Basic Experiments, cont.

• Prettest-Posttest Design
• Participants are given a pretest before the
  experimental manipulation is introduced
• Pretest sensitization is a potential problem

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The Solomon Design

• Uses a combination of the posttest-only and
  pretest-posttest design

Pretested?
19
The Solomon Design, cont.
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Participant-Related Artifacts

• Artifact
• Good subject
• Evaluation apprehension
• How to Overcome?

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Experimenter Expectancy Effects

• Systematic error/bias resulting from the
  uncontrolled intentions or actions of the
  experimenter
• Rosenthal Fodes (1963) study of maze-blind vs.
  maze bright rats

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How to Control Experimenter Expectancy Effects

• Blind vs. Double-Blind Procedures
• Blind Experimenters
• Double-Blind Procedure

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Experiments Realism

• Experiments are often criticized because of their
  artificial nature
• Can we really generalize the results from our
  experiments to the real world?
• Mook article
• Consider an example

24
Aschs (1955) Study of Conformity

• Ps told they were taking part in a study of
  visual perception
• Asked to make judgments about the lengths of lines

Standard
A B C
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Experiments Realism, cont.

• Two Forms of Realism
• Mundane Realism
• Experimental Realism

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Tuesday

• Between-Subjects Designs
• Cozby, Chapter 8