1. Class 8 Spring 2017 Ang &Huan (2006)
Chapter Mediation
Class 8 Spring 2017
Ang &Huan (2006)

3. Moderator vs. Mediator Moderator variable (“separator”) Mediator
When or for whom a variable X most strongly predicts an outcome (criterion) variable Y (strength and direction + or -)
Mediator
The mechanism by which a predictor causes or explains the outcome

4. Moderation Analyses: Regression
P: Alcohol use
M: Gender Depression
Alcohol Use X
Gender M F

5. Mediation
Establishes How or Why a variable causes or predicts the criterion (or outcome) variable.
Mediator is the mechanism by which predictor causes or explains the outcome
Predictor Outcome
Predictor  Mediator ---Outcome
Parent Drinking----F. Conflict - Low Self Esteem

6. Mediation: Baron & Kenny (1986) The Beginning Modelc Y X

7. The Mediational Model M b a c' Y X

8. Baron and Kenny procedure
X  Y (test path c)
 M (test path a)
M (and X)  Y (test path b)
X (and M)  Y (test path c′ )
Analyses 3 and 4 use the same regression equation.

9. Sobel Test Calculator http://www.psych.ku.edu/preacher/sobel/sobel.htm
Whether the indirect effect of the predictor on the criterion via the mediator is significantly different from zero
Numbers needed
a = raw (unstandardized) regression coefficient for the association between predictor and mediator.
sa = standard error of a.
b = raw coefficient for the association between the mediator and the outcome (when the predictor is also a predictor of the DV).
sb = standard error of b.

10. Ang & Huan (2012) b a c

11. Ang & Huan (2012) b a c C” Suicidal Ideation Academic stress
Depression b a c
Suicidal Ideation
Academic stress C”

12. Depression
a b C
Academic Stress Suicidal ideation C’

13. Depression
r = a =.25** r = .62**/b=.60**
C’ =.22**
Academic Stress Suicidal ideation
C =.07*

14. Mediation Model Ang & Huan (2006)

15. Strength of Mediated Effect
Sobel Test- Indicated if change in academic stress Bs from Path c to path c’ is statistically significant
Shrout & Bolger (2002)
Proportion of relation of academic stress to suicide ideation that is mediated by depression
Calculated from the unstandardized Bs for paths ab& c; requires a sample size of about 500
ab/c = ( ) ( )/ ( ) = ( ) / ( ) = = 74%

16. Strength of Mediated Effect
Sobel Test- Indicated if change in academic stress Bs from Path c to path c’ is statistically significant
Shrout & Bolger (2002)
Proportion of relation of academic stress to suicide ideation that is mediated by depression
ab/c = (.12) (2.71)/.44 = /.44 = = 74%

17. Mediation VS Indirect Effects

18. Class Example b a c Self-Reported Drinking Drinking Attitudes
Friends’ Drinking b a
Self-Reported Drinking c
Drinking Attitudes

19. Friends’ Drinking
a =.88*** r=.49**/b=.12ns
C’ = .53**
Self- Drinking Drinking Attitudes
C’=.43**

20. Path Analyses

21. SEM Model

22. Person Centered Approach
Identify groups of people who are similar and different
Cluster Analysis
Latent Class Profile Analyses
Growth Mixture Analyses

24. Latent Profile/Class Analyses
Identify subgroups of people based on individual characteristics
Profile - Continuous measure
Class- Categorical measure
Calculate probabilities of being in each group-

25. Growth Mixture Modeling