Abstract
Suicide is one of the leading causes of death worldwide. The incidence rate of suicide, particularly among young people, is still high in New Zealand. A great amount of research on suicidality has identified some risk factors for suicidal ideation and suicide attempts. However, these research results have not yet been translated into effective strategies of prevention or intervention. The interpersonal theory of suicide—one of the most studied theories of suicide—attempts to integrate risk factors of suicide into a causal pathway. The theory assumes that thwarted belonging and perceived burden are equally important and are the most proximal mental states in the development of suicidal ideation. Although a number of studies have provided evidence to support the interpersonal theory, the results have been mixed. The present thesis aimed to examine the controversial parts of the interpersonal theory regarding the relationships among thwarted belonging, perceived burden, and active suicidal ideation using a 4-wave longitudinal survey among 298 undergraduate students.
In Study 1, a cross-sectional analysis of baseline data was conducted to test the proposed hypotheses. The results showed that thwarted belonging had no direct influence on active ideation. Perceived burden was found to both mediate and moderate the relationship between thwarted belonging and active ideation. In Study 2, the cross-lagged panel model (CLPM) and single-level random-effects CLPM (RE-CLPM) were used to test the mediation hypothesis with longitudinal data. The cross-sectional results, however, could not be confirmed in this longitudinal mediation analysis. Similarly, in Study 3, the moderation effect in the cross-sectional study could not be confirmed using either the CLPM or RE-CLPM analyses. In Study 4, a post-hoc analysis of the longitudinal data used in Study 2 and Study 3 was conducted to test whether the follow-up interval between perceived burden and active ideation could influence the relationship between perceived burden and active ideation, and also the mediation and moderation effects. When the follow-up period was shortened to concurrency, the relationship between perceived burden and active ideation was stronger, and the moderation and mediation effects showed significant in the RE-CLPM models, after controlling autoregression for each variable.
Overall, these results provide support that thwarted belonging has an indirect effect on active ideation. Additionally, the new mediation hypothesis—that the relationship between thwarted belonging and active ideation was mediated by perceived burden—obtained support only when the time interval between perceived burden and active ideation was concurrent. Similarly, the moderation hypothesis—that the interaction of thwarted belonging and perceived burden influences active ideation—also obtained support under the same circumstance. The findings in the thesis have significant implications in the psychological mechanisms and the prevention and intervention of suicide. Finally, it will be a fruitful avenue for future studies to confirm the results and overcome the issues raised in the thesis.