1. Can a Variable be both a Mediator and a Moderator? Dominique Muller (University of Grenoble/University Institute of France) Charles M. Judd (University of Colorado) Vincent Yzerbyt (Catholic University of Louvain)

2. 2 Mediation ( Baron & Kenny, 1986; Judd & Kenny, 1981 )  X is a treatment and units are randomly assigned to conditions  Me is a mediator measured after X (and before Y)  Y is the dependent variable

3. 3 X Y Me Mediation X Y

4. 4 X Y Me Mediation Without a causal argument, these are nothing else than regression equations, not a strong case for mediation Social psychologists have been very concerned with causality in mediation models (e.g., Spencer, Zanna, & Fong, 2005)

5. 5 Mediation in the MacArthur approach The MacArthur approach (see Kraemer, Kiernan, Essex, & Kupfer, 2008) takes its root in clinical interventions and randomized clinical trials (RCT) c, a, and b conjointly significant or c, a, and d conjointly significant Mediation

6. 6 Moderation in social psychology S Y P

7. 7 P Y S

8. 8 S Y P P Y S Social psychologists are fine with both models Only preferences dictate which one will be used Moderation in social psychology Moderation is equated with simply a statistical interaction

9. 9  X is a treatment and units are randomly assigned to conditions  Mo, the moderator, is measured PRIOR to the treatment  And therefore, the Treatment and the moderator are uncorrelated Moderation in the Mac Arthur approach Moderation is not the same as simply a statistical interaction

10. 10 In social psychology: Definition of moderation In Mac Arthur Approach: A moderator P is a variable that affects a S – Y relationship or a moderator S is a variable that affects a P – Y relationship A moderator is a variable that affects a causal effect of X on Y

11. 11 Can a variable be both a mediator and a moderator? From a social psychology perspective: -> Me is a mediator (c, a, and b are conjointly significant) -> Me is a moderator (the d interaction is significant) For the MacArthur approach: -> Me is only a mediator (c, a, and d are conjointly significant)

12. 12 XY Me For social psychologists

13. 13 XY Me This explains why it has been argued that this is a case of moderated mediation (Preacher, Rucker, & Hayes, 2007) For social psychologists

14. 14 XY Me XMe For the MacArthur approach

15. 15 XY Me XY XY XMe Can a variable be both a mediator and a moderator? Social psychology perspective MacArthur Approach

16. 16 Conclusion Can a variable be both a mediator and a moderator? Yes, it can be both if moderation and statistical interactions are equated No, if moderation and statistical interactions are not equated How should we define moderation?