This thesis contains a single volume composed of five chapters and is submitted to the University of Birmingham to satisfy requirements for the degree of Doctorate of Clinical Psychology. This thesis includes a literature review, an empirical research paper and two corresponding press releases providing brief summaries of each piece of work in language suitable for a lay audience.

Literature Review
The literature review section features a meta-analysis of anxiety and depressive disorder prevalence rates among young autistic people. The impact of moderators is explored and sources of heterogeneity are discussed.

Empirical Research Paper
The empirical research paper describes a study conducted to explore the relationship between depressive symptoms, autistic traits and sleep difficulties. Theoretical and clinical implications are discussed.