The results of the review were as follows:
Colonoscopic sensitivity to detect:
CRC, 95%;
large polyps (larger than 1cm), 85%;
intermediate polyps (6-9mm), 80%; and
small polyps (smaller than 5mm), 75%.
Colonoscopic complication rates were:
postpolypectomy haemorrhage, 0.3%;
perforation, 0.1%;
mortality, 0.02%; and
utilities (comprehensively reported in the paper).
Lifetime risk of CRC was represented by a bounded Johnson distribution; mean value for men 6% and mean value for women 5.5%. The mode of the Johnson distribution was set to 0.5%, close to zero to represent the low risk attached to developing CRC in a patients lifetime. Incidences of adenomas were assigned to 'fast-progressing' or 'slow progressing' groups in a proportion that was age dependent. The assumption was made that less than 2.5% of adenomas become CRC within the first ten years. The time of transition from one state to another was determined by random allocation to one of two different bounded Johnson distributions representing the progression rate. Fast progressing adenomas transition to CRC had a mean period of 26 years. Slow progressing adenomas transition to CRC had a mean period of 52 years.
Whilst transitioning from adenoma to CRC the model allows adenomas to simultaneously make transitions in size from small, to intermediate and on to large. These parameters were again represented individually by bounded Johnson distributions that were dependent upon gender, rate of progression (fast versus slow) and the size transition taking place (small to intermediate or intermediate to large), thus allowing all adenomas the possibility of making the transition to CRC whilst favouring those which are more likely to do so.
Asymptomatic CRC progressed towards symptomatic CRC using a normal distribution with a mean value of 4.8 years. Asymptomatic CRC was initially assigned to the 'local' stage. CRC could then make the transition to 'regional' stage (mean value 5.2 years) or 'distant' stage (mean value 5.55 years) using a normal distribution. This method allowed transition from 'local' to either of the other transition stages. Once the transition to 'distant' stage had been made the patient would remain in this transition state until death.