The Importance of Testing Mediation and Moderation

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The Importance of Testing Mediation and Moderation

• Jon A. Krosnick
• Departments of Communication,
• Political Science,
• and Psychology
• Stanford University

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Outline for Today

• Introduction Defining and Testing Mediation and
  Moderation
• Example News Media Priming
• Example Public Learning About Policy Issues

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Introduction
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The Audience Participation Portion of Todays Show
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What is a moderator?- Definition- Example of
moderation What is a mediator?- Definition-
Example of mediation
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Moderator A variable that changes the impact of
one variable on another. Predictor Outcome
Moderator
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Testing a Moderator Hypothesis
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Dont Presume Linearity
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Mediator The mechanism by which one variable
affects another variable
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Testing Mediation

• Step 1 IV DV
• Step 2 IV Mediator
• Step 3 Mediator DV
• Step 4 Effect of IV on DV is significantly
  reduced by controlling for the mediator
• Sobel (1982) test (http//www.unc.edu/preacher/so
  bel/sobel.htm)
• Goodman (1960) test
• On the exact variance of products. Journal of
  the American Statistical Association, 55,
  708-713.

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First Example

• News Media Priming

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News Media Priming

• News media attention to an issue increases the
  impact of performance assessments in the domain
  on overall presidential evaluations.

Media Attention to Unemployment
Presidential Performance Handling Unemployment
Overall Presidential Performance
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Mediation of Moderation
Media Attention to Unemployment
Accessibility of Unemployment Performan
ce Assessment
Unemployment Presidential Performance
Overall Presidential Performance
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Unemployment Attitudes
Unemployment
Unemployment Story
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Study Design

• Pre-exposure questionnaire
• - 5 non-political TV news stories
• 2 stories on either
• Crime Pollution Unemployment
• Post-exposure questionnaire

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Measures

• Overall presidential performance
• Presidential performance handling
• Crime
• Pollution
• Unemployment
• Accessibility (response latency)
• Political knowledge
• Trust in the news media

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Moderation of Mediation of Moderation!
Not Mere Accessibility Persuasion?
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Media Attention to Unemployment
Belief that Media Personnel Believe the Issue is
Important for the Nation
Trust in the Media
Political Knowledge
Belief that the Issue is Important for the Nation
Unemployment Presidential Performance
Overall Presidential Performance
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Conclusion

• Understanding moderation and mediation increase
  confidence in the causality claim
• Understanding mediation changed the political
  character of the effect (not victims of the
  architecture of the mind)
• Understanding moderation changed the normative
  spin of the effect (not naïve people who lack
  political expertise people choose to be
  influenced)

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Example Two

• How Do People Learn About Politics?

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October 13, 1988 Presidential Debate George H. W.
Bush vs. Michael Dukakis
Day Before 134 people interviewed Day After 63
reinterviewed - Cued Recall - Recognition
Memory - Attitude Importance
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Analysis Hierarchical Linear Modeling

• Participant
• Taxes Capital Defense
• Punishment Spending
• CR RM CR RM CR RM

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Effect of Importance on Knowledge

• b.46
• SE.23
• plt.05
• N366

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The Usual Approach

• Stop There.
• Smile.
• Fold Up Tent.
• Go Home.

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Laboratory Experiment Conditions Unpaced
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Candidate A
A woman should have the right to obtain an
abortion if she so chooses. The death penalty is
an acceptable punishment for convicted
murderers. We should build more nuclear power
plants to provide an alternative source of
energy. The U.S. should send more troops to
Saudi Arabia to oppose Iraqs invasion of
Kuwait.   In order to protect American jobs, we
need more restrictions on the number of goods
imported.
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Laboratory Experiment Conditions Unpaced Paced
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You will have 20 seconds to read five statements
made by each candidate. After 20 seconds, the
statements will disappear, so read as quickly as
you can.
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Laboratory Experiment Conditions Unpaced Paced El
aboration Time
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You will have 20 seconds to read five statements
made by each candidate. After 20 seconds, the
statements will disappear, so read as quickly as
you can. Once the statements disappear, you
will have 45 seconds to think about what you
read.
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Laboratory Experiment Conditions Unpaced Paced El
aboration Time Topic Labels
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Candidate A
Abortion
A woman should have the right to obtain an
abortion if she so chooses. The death penalty
is an acceptable punishment for convicted
murderers. We should build more nuclear power
plants to provide an alternative source of
energy. The U.S. should send more troops to
Saudi Arabia to oppose Iraqs invasion of
Kuwait.   In order to protect American jobs, we
need more restrictions on the number of goods
imported.
Death Penalty
Nuclear Power
Iraq
Imports
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Measures

• Free Recall
• Recognition Memory
• Attitude Importance

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Alternative Hypothesis
Actual Knowledge Volume
Perceived Knowledge Volume
Attitude Importance
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Conclusions

• You can test mediation with panel data
• You can test mediation via moderation
  manipulations in the lab
• You can test mediation with cross-sectional data
  with instrumental variables and 2SLS

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Broader Conclusion

• Test mediation (and moderation)!
• Two examples where this was not done
• Valentino, N. A., Hutchings, V. L., White, I.
  K. (2002). Cues that matter How political ads
  prime racial attitudes during campaigns. American
  Political Science Review,96, 75-90.
• Tali Mendelberg The Race Card Campaign Strategy,
  Implicit Messages, and the Norm of Equality
  (Princeton Univ Press, 2001).