How to predict participation in colorectal cancer screening ? The contribution of Theory of Planned Behaviour.

Summary Background: Detected early, colorectal cancer can be cured in nine cases out of ten, but it remains the second leading cause of cancer mortality in France. However, current participations in organized screening continue to be low and must be improved. Based on the Theory of Planned Behaviour (TPB, Ajzen, 1994), this study aims to identify the psychosocial determinants of participation in organized screening for colorectal cancer.Methods: Two qualitative studies were previously conducted with GPs and patients to develop a questionnaire measuring salient beliefs related to attitudes, subjective norms and perceived behavioural control toward colorectal cancer screening (Ajzen, 2006). Participants in the present study came from the general population (men and women aged between 50 and 74) and were recruited through a screening structure. Ultimately, 160 questionnaires were collected. All TPB determinants were measured at baseline, screening behaviour was evaluated 4 months later. A path analysis with a Bayesian estimator was applied to examine the hypothesized model.Findings: Analysis revealed that model fit was acceptable (predictive p-value = .54). The model explained 35% of intentions and 6 % of screening behaviour. Both subjective norms (β = .26, 95% CI [.10, .40])and perceived behavioural control (β = .38, 95% CI [.20, .54]) were related to intentions. Only perceived behavioural control was significantly related to screening behaviour (β=.21, 95% CI [.01, .40]).Discussion: This study highlighted the importance ofperceived behavioural control in colorectal cancer screening participation. Future researches focusing on intention-behaviour gap would be necessary.