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. Outline for Today. Introduction: Defining and Testing Mediation and Moderation Example: News Media Priming

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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


Outline for Today

  • Introduction: Defining and Testing Mediation and Moderation

  • Example: News Media Priming

  • Example: Public Learning About Policy Issues


Introduction


The Audience Participation Portion of Today’s Show


What is a moderator?- Definition- Example of moderationWhat is a mediator?- Definition- Example of mediation


Moderator

A variable that changes the impact of one variable on another.

PredictorOutcome

Moderator


Testing a Moderator Hypothesis


Don’t Presume Linearity


Mediator

The mechanism by which one variable affects another variable


Testing Mediation

  • Step 1: IVDV

  • Step 2: IVMediator

  • Step 3: MediatorDV

  • Step 4: Effect of IV on DV is significantly reduced by controlling for the mediator:

    • Sobel (1982) test (http://www.unc.edu/~preacher/sobel/sobel.htm)

    • Goodman (1960) test

      On the exact variance of products. Journal of the American Statistical Association, 55, 708-713.


First Example:

News Media Priming


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


Mediation of Moderation

Media Attention to Unemployment

Accessibility of Unemployment

Performance Assessment

Unemployment Presidential Performance

Overall Presidential Performance


Unemployment

Attitudes

Unemployment

Unemployment

Story


Study Design

  • Pre-exposure questionnaire

  • - 5 non-political TV news stories

  • 2 stories on either:

    • Crime Pollution Unemployment

  • Post-exposure questionnaire


Measures

  • Overall presidential performance

  • Presidential performance handling:

    • Crime

    • Pollution

    • Unemployment

  • Accessibility (response latency)

  • Political knowledge

  • Trust in the news media


Not Mere Accessibility – Persuasion?

Moderation of Mediation of Moderation!


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


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)


Example Two:

How Do People Learn About Politics?


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


Analysis: Hierarchical Linear Modeling

Participant

TaxesCapital Defense

PunishmentSpending

CR RMCR RMCRRM


Effect of Importance on Knowledge

b=.46

SE=.23

p<.05

N=366


The Usual Approach

Stop There.

Smile.

Fold Up Tent.

Go Home.


.44

.11*

.04

.31**


Laboratory Experiment Conditions

Unpaced


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 Iraq’s invasion of Kuwait.

In order to protect American jobs, we need more restrictions on the number of goods imported.


Laboratory Experiment Conditions

Unpaced

Paced


“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.”


Laboratory Experiment Conditions

Unpaced

Paced

Elaboration Time


“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.”


Laboratory Experiment Conditions

Unpaced

Paced

Elaboration Time

Topic Labels


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 Iraq’s 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


Measures

  • Free Recall

  • Recognition Memory

  • Attitude Importance


Alternative Hypothesis

Actual

Knowledge

Volume

Perceived

Knowledge

Volume

Attitude Importance


.37*

.27*

.00

.55**

.04

.38*


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


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).


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