Roberts, RachelProeve, MichaelWilliams, Sarah Elizabeth2023-11-292023-11-292023https://hdl.handle.net/2440/140003In this thesis, the aim was to identify the main predictors of dissolution, distress, and restoration of close and best friendships in adulthood. A second aim was to identify predictors of actor-ostracism of current and former close friends. A wide range of factors found to impact outcomes in romantic relationships and child/adolescent friendships in the literature were explored using prospective, current perspective, and retrospective designs. Data were collected in three waves over a 12-month period. The sample comprised fluent English speakers ranging from younger to older adulthood and spanned 28 countries of residence. The results showed that close and best friends were able to predict one another’s ratings of friendship quality with high accuracy, and that there was high inter-rater agreement of friendship quality within these friendships. Inter-rater agreement of friendship quality was highest for reciprocated best friendships, followed by bestclose friendships, and then reciprocated close friendships. Substantial contemplation of engagement in intervention programs targeting maintenance and restoration of close friendships was demonstrated in the sample. Univariate regression analyses demonstrated that close and best adult friendships were impacted by similar factors to both romantic relationships and child/adolescent friendships. A series of multiple regression analyses identified two major themes of predictors across all outcomes: bullying behaviours within peer groups and dyads (ostracism and verbal victimisation), and sexual interest between romantic couples and dyads. While the former uniformly predicted poorer friendship outcomes, the latter predicted higher friendship instability, including higher dissolution, distress, and ostracism, but also predicted higher likelihood of restoration. Practical and research implications include the importance of identifying bullying behaviours and sexual interest factors (within-dyads or romantic-partner) in the therapy context and incorporating these themes in the development of friendship-based intervention programs for adults.enFriendshipadulthoodreciprocationdissolutiondistressostracismrestorationThesis