Understanding the factors and mechanisms that influence colorectal cancer screening uptake among socially deprived and non-deprived populations.

Colorectal cancer (CRC) is the second most common cause of cancer death in the UK. Since the introduction of the NHS Bowel Cancer Screening Programme CRC incidence and mortality rates have reduced, however, screening uptake in the overall population remains suboptimal and is disproportionately low among populations with low socioeconomic status (SES) and Black and Minority Ethnic populations. This thesis aimed to critically assess the available evidence of public health interventions to improve CRC screening and to examine the possible mechanisms of socioeconomic inequalities in CRC screening uptake within a UK setting.
A systematic review and meta-analysis (Study 1) of randomised controlled trials (RCTs) to increase CRC screening uptake was conducted. Data from 102 RCTs including 1.94 million participants were analysed and intervention effectiveness was examined by level of SES. Interventions significantly improved screening uptake, especially among low SES populations, and helped reduce - but not eliminate - SES disparities. Specific intervention strategies were highlighted as effective among low SES groups.
Study 2 used qualitative interviews (N = 27) to explore the views of different socioeconomic and sociodemographic population subgroups and identify the barriers and facilitators to CRC screening. Results highlighted both practical and emotional factors that influenced screening decisions and revealed both similarities and differences in the views of different subgroups. Study 3 used cross-sectional, observational, survey data (N = 206) to explore key sociodemographic and psychosocial variables as potential moderators and mediators of screening intention. Results indicated that psychosocial variables mediated the effects of past behaviour on screening intention and identified some differences by educational attainment and area-level deprivation.
This thesis argues the importance of considering both sociodemographic and psychosocial factors in relation to improving CRC screening uptake and reducing inequalities. Results highlighted key determinants of CRC screening participation and identified specific pathways via which sociodemographic and psychosocial variables interact to affect screening intention. This thesis provides an evidentiary basis that can be used to inform future public health initiatives and/or interventions that aim to reduce the CRC inequality gap.