1. Center for Developmental Research
Örebro University, Sweden
Maarten van Zalk, Lauree Tilton-Weaver, Margaret Kerr, Håkan Stattin, Nejra van Zalk

2. Overview Our main interests Current SIENA studies
Main issues & many wishes

3. Personal interests

4. Interests Online vs. offline networks (Maarten)
Personality: psychopathic traits, Big Five (Maarten, Margaret)
Externalizing: delinquency, bullying, aggression (Margaret, Håkan, Lauree)
Internalizing: depression, social anxiety (Maarten, Nejra)
Parents, peers, & externalizing (Lauree)

5. Data Seven Schools: up to 8 friends in the school (N = 2,500)
Political Socialization Program: Up to 10 friends in school (N = 4,500)
10-to-18: large community, up to 23 friends, romantic partners, and siblings in the community (N = 4,500)
ONLINE vs.OFFLINE: small community & 89% of all friends found exclusively online (N = 700)
ALL data also have independent parental reports

6. Recent publications
Kerr, M, Van Zalk, M., Stattin, H. (in press). Psychopathic traits moderate peer influence on delinquency. Journal of Child Psychology and Psychiatry.
Van Zalk, N., Van Zalk, M., Kerr, M. & Stattin, H. (in press). Socialization of social anxiety in adolescent crowds: Punks, goths, and other eye-catching peer crowds revisited. Journal of Abnormal Child Psychology.
Van Zalk, N., Van Zalk, M., Kerr, M. & Stattin, H. (2011). Social anxiety as basis for friendship selection and socialization in a youth social network. Journal of Personality, 29,
Van Zalk, M., Kerr, M.. Branje, S., Stattin, Håkan, & Meeus, W. (2010). Peer contagion and adolescent depression: The role of failure anticipation. Journal of Clinical Child and Adolescent Psychology, 39,
Van Zalk M., Branje, S. Kerr, M.,Stattin, H., & Meeus, M. (2010). It takes three: Selection, influence, and de-selection processes of depression in adolescent peer networks. Developmental Psychology, 46,

7. Issues & Wishes Moderation / Interaction effects
Mediation / Indirect effects

8. Plotting Simple Slopes
Y' = b1(x1-x1^) + b2(x2-x2^) + b3((x1-x1^)(x2-x2^))
b1 = IV (parenting-ego estimate) b2 = Moderator (delinquency-alter estimate) b3 = Interaction: parenting-ego×delinquency-alter estimate
For x1^ the average parenting score was used
For x2^ the average delinquency score was used

9. Moderation Approach to graphing: Plot simple slopes
Is there a user-friendly way to visualize and test differences between groups?
Is this the best for two variables with a wide range of values?
Average scores or average for ego/alter?
If only for ego or alters, how do you get this information?
Are ego-alter tables the way to go?
Wish: Function in RSiena that can help visualize interaction effects, visualize the slopes for the different effects

10. Mediation Processes / mechanisms underlying peer influence effects
Crucial for understanding how peer influence works
Stages in influence
Indirect effects

11. Mediation
Do negative cognitions mediate peer influence on depressive symptoms?
Traditional conditions for mediation:
X on Y
X on Z
When X and Z together on Y, only X remains

12. Mediation
Do negative cognitions mediate peer influence on depressive symptoms?
Recently:
Indirect effects of X on Y VIA Z
Negative cognitions
Friends depr
Targets’ depression

13. Mediation .74*** .43*** .12*** Depressive symptoms Cognitions
Behavioral evolution (influence)
Parameter
s.e.
Rate period 1
***
1.79
8.1231***
1.43
Rate period 2
***
1.89
8.975***
1.31
Linear shape
1.21***
.24
1.45***
.23
Quadratic shape
1.12***
1.81***
.33
Ego’s negative cognitions
.43***
.08
Average alter
.12***
.04
.74***
.12
.74***
.43***
Negative cognitions
.12***
Average alt
Targets’ depression

14. Mediation Indirect effects of X on Y VIA Z .74*** .43*** .12***
Can we use a Sobel’s test?
Boots-trapping?
.74***
.43***
Negative cognitions
.12***
Average alt
Targets’ depression

15. Overview Our main interests Current SIENA studies
Main issues & many wishes