PhD Oral Defence - Melisa Castellanos, Psychology

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This dissertation reports the results from two studies conducted with a sample of 1595 fourth, fifth and sixth graders from nine schools in Bogotá, Colombia (Mage= 10.25 years), who completed peer nomination measures of social behaviours at two measurement points. The main objective was to examinee homotypic (i.e. the effect of early adolescents’ behaviours on one dimension on the same dimension measured for their friend at a later time) and heterotypic peer effects (i.e. the effect of early adolescents’ behaviours at an initial time on their friend’s subsequent levels on another behaviour) among stable dyadic friendship relationships. Specifically, two types of aggressive behaviour (physical and relational) and one type of prosocial behaviour (help) were analyzed. Additionally, the moderating roles of gender, popularity and group norms were examined.

A structural equation modelling approach was used to achieve the objectives. Specifically, the Actor-Partner Interdependence Model (APIM) was used to estimate peer effects at the dyadic level, and Latent Profile Analyses were used to explore salience group norms at the classroom level context. Moreover, these peer effects were compared by gender, popularity and classroom salience norms (i.e. classroom-level association between popularity and the behaviours).

It was observed that the two types of aggressive behaviour, as well as help, increased as a function of the best friend’s level of those behaviours. Moreover, it was demonstrated that peer heterotypic influence effects did not occur between help and physical aggression, while friends’ levels of relational aggression predicted increases in pre-adolescents’ levels of help. Structural multi-group comparisons revealed that the most popular pre-adolescents exerted a larger influence on their best friends’ aggressive behaviour. In addition, girls seemed more prone to friend’s influence for aggression whereas boys were exclusively prone to increase their levels of help as a result of engaging in friendships with physically aggressive peers.

Regarding the moderator role of salience norms, the results revealed that homotypic peer influence effects of physical aggression and help were stronger in classrooms in which these behaviours were equally salient. Similarly, heterotypic peer effects among relational aggression and help occurred only in these types of classrooms.