Figure 1

This flowchart demonstrates how the different positivity patterns generated by the three kits create 55 positivity combinations. The BCSP algorithm deals with these combinations differently depending on the spot pattern and SP%. There were subjects with an unclear kit one and normal results in kits two and three that are returned to the screening programme with a higher SP% than some weak positive combinations leading to colonoscopy. These weak positive combinations derive from an unclear result in kit one followed by some positive spots in either kit two or three.