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Background: Daily nebuliser use is crucial for people with cystic fibrosis (CF) to stay healthy, but average adherence is only 35-50%. Making nebuliser use ‘habitual’ (i.e. automatic) may aid adherence, but extant CF literature has mainly focused on treatment burden and factors involving conscious deliberation. This thesis aims to explore a broad range of clinical and psychological factors that are potentially associated with objective nebuliser adherence among adults with CF. Methods: This thesis encompassed three studies. First, a retrospective analysis of adherence data captured using chipped nebulisers from 2013-2016 among 126 adults was performed to explore relevant clinical factors. Second, a mixed-methods study was performed among 20 adults to identify the psychological factors differentiating high or low nebuliser adherence patterns (i.e. ≥80% or < 50% of all nebulised treatments over one year). Third, a secondary quantitative analysis was performed using data from a two-centre pilot adherence trial among 64 adults to replicate findings from the mixed-methods study. Results: The retrospective analysis showed a U-shape relationship between adherence and age, with lowest adherence levels among adults aged 19-25 years. Lower adherence was also noted for long term (>3 months) nebuliser regimen in comparison to shorter-term treatments. The mixed-methods study found stronger habit and greater opportunities among high adherers, though habit and perceived opportunity scores were highly positive correlated. Habit attenuated the relationship between treatment complexity and perceived treatment burden. Indeed, in interviews, high adherers reported that routinisation and greater automaticity made treatment burden more manageable. The secondary analysis using pilot trial data found stronger habit and lower concerns among high adherers. In an ordinal regression model, only habit strength was independently associated with adherence. Conclusion: Adherence to long-term CF nebuliser treatments is problematic, especially among younger adults with CF. Habit may attenuate perceived burden and is a promising target for adherence interventions.

The increasing prevalence of childhood obesity in the United Kingdom is of great interest to public health policy makers and guidance developers such as NICE, as well as the general public. In order to develop effective policies, the causes of childhood obesity need to be better understood. Analysing the Millennium Cohort Survey, this thesis uses econometric techniques to investigate the relationships between childhood obesity, family lifestyle behaviours and child health outcomes. The first empirical chapter investigates the causal effects of breastfeeding behaviours on obesity during early childhood, a topic which has been of particular interest to NICE. There is a small but statistically significant influence suggesting that breastfeeding should be one part of a wider effort to reduce obesity by influencing lifestyle, such as Change4Life. These effects appear to increase in magnitude and significance as children get older suggesting that the dynamics of lifestyle and childhood obesity should be investigated further. The second empirical chapter investigates the relationship between underlying family lifestyle and childhood obesity using a dynamic framework. Childhood obesity is one of the strongest predictors of obesity in adulthood. If lifestyle is learnt in childhood and is persistent then this could exacerbate the problem of childhood obesity. Amongst other findings, this chapter concludes that childhood weight status significantly depends on family lifestyle. The final empirical chapter extends this model and allows the effects of both family lifestyle and underlying health on childhood obesity to be investigated. Childhood weight is a significant outcome measure of underlying child health after the age of five. The results suggest that policies should target various lifestyle behaviours simultaneously by improving underlying lifestyle through education and improved understanding and enabling families to make positive changes.