Quantifying public preferences for different bowel preparation options prior to screening CT colonography: a discrete choice experiment

OBJECTIVES CT colonography (CTC) may be an acceptable test for colorectal cancer screening but bowel preparation can be a barrier to uptake. This study tested the hypothesis that prospective screening invitees would prefer full-laxative preparation with higher sensitivity and specificity for polyps, despite greater burden, over less burdensome reduced-laxative or non-laxative alternatives with lower sensitivity and specificity. DESIGN Discrete choice experiment. SETTING Online, web-based survey. PARTICIPANTS 2819 adults (45-54 years) from the UK responded to an online invitation to take part in a cancer screening study. Quota sampling ensured that the sample reflected key demographics of the target population and had no relevant bowel disease or medical qualifications. The analysis comprised 607 participants. INTERVENTIONS After receiving information about screening and CTC, participants completed 3-4 choice scenarios. Scenarios showed two hypothetical forms of CTC with different permutations of three attributes: preparation, sensitivity and specificity for polyps. PRIMARY OUTCOME MEASURES Participants considered the trade-offs in each scenario and stated their preferred test (or chose neither). RESULTS Preparation and sensitivity for polyps were both significant predictors of preferences (coefficients: -3.834 to -6.346 for preparation, 0.207-0.257 for sensitivity; p<0.0005). These attributes predicted preferences to a similar extent. Realistic specificity values were non-significant (-0.002 to 0.025; p=0.953). Contrary to our hypothesis, probabilities of selecting tests were similar for realistic forms of full-laxative, reduced-laxative and non-laxative preparations (0.362-0.421). However, they were substantially higher for hypothetical improved forms of reduced-laxative or non-laxative preparations with better sensitivity for polyps (0.584-0.837). CONCLUSIONS Uptake of CTC following non-laxative or reduced-laxative preparations is unlikely to be greater than following full-laxative preparation as perceived gains from reduced burden may be diminished by reduced sensitivity. However, both attributes are important so a more sensitive form of reduced-laxative or non-laxative preparation might improve uptake substantially.