Literature suggests a relationship between sleep problems and behaviours that challenge (BTC) among adults with Intellectual Disabilities (ID), but the nature of these relationships remains unclear. People with ID may be more susceptible to types of sleep disorders; however, differences in communication and how diagnostic criteria are currently defined make this difficult to clarify. BTC are a common presentation in clinical practice, and the extent to which sleep problems contribute to them is unclear. The overall aim of the thesis is to examine whether sleep problems are implicated in the cause of BTC.

Two systematic reviews, a service evaluation, and a mixed methods study were conducted. The first systematic review on the prevalence of sleep disorders among adults with ID identified a lack of precision due to inadequate definitions and measurement. The second systematic review found limited good-quality sleep intervention studies among adults with ID. The service evaluation found that behaviours that challenge co-occur frequently with disordered sleep. The mixed methods study utilised actigraphy with 27 adults with ID over 441 nights and interviewed 16 adults with ID and their carers. The quantitative analysis found that sleep onset latency did predict behaviours that challenge occurring on subsequent days, though the effect was small. As a result of combining qualitative and quantitative findings, a relationship was found between delays to sleep onset or a delayed sleep wake phase and further daytime consequences, including reduced daytime activity, irritability, and increased anxiety.

In summary, the results of this thesis suggest that sleep difficulties have a less significant role in predicting behaviours that challenge than was expected and they seem unlikely to be a major cause of these difficulties. Methodological and definitional difficulties in studying these relationships are discussed. Delays in sleep onset and a delayed sleep-wake phase should be considered in clinical practice due to the relationship identified with other daytime consequences.