Open to screen: Optimising invitation letters to increase participation in the National Bowel Cancer Screening Program

The Australian National Bowel Cancer Screening Program (NBCSP) invites eligible Australians aged 45 to 74 years to undergo a biennial at-home bowel cancer screening test. Despite its proven effectiveness in enhancing early detection and reducing mortality, participation remains low (42% in 2023-2023). The NBCSP uses an “advance notification” letter followed by an “invitation” letter to encourage participation, but research on how best to design these letters is limited. This thesis aimed to optimise these letters using insights from invitees and behavioural theory. Study One used a scoping review to summarise the characteristics of advance notifications aimed at increasing cancer screening. No distinguishing features of effective (versus ineffective) notifications were identified, suggesting that individual factors may also influence their impact. Study Two tested two redesigned advance notification letters, targeting screening barriers and enablers, compared to the current NBCSP letter. No significant difference was found in screening intention between the current and redesigned letters, but for participants with high barriers and low enablers, the redesigned letters were less effective. Study Three interviewed NBCSP invitees, revealing that the current letters were perceived as inaccessible and unengaging. Participants expressed a need for clearer guidance in the letters on how to complete the screening test. Finally, Study Four tested a redesigned invitation letter compared to the current NBCSP version via online survey. This letter significantly increased screening likelihood, mediated by increased selfefficacy, perceived benefits, and action planning. These effects varied by prior screening history and gender. Behavioural theory suggests that advance notification and invitation letters should focus on intention formation and action planning, respectively. Tailored messaging and useability enhancements can further increase effectiveness.