Targets play an increasing role in medicine. Using the recent target of caecal intubation in over 90% of colonoscopies,¹ I herewith outline some statistical issues implicated. Typical trainees need three years to achieve competence. CUSUMs² are useful in assessing progress during the learning curve, but “test endoscopies” are needed to calculate and prove performance statistically more robust. But how many?

A trainee at the end of his learning curve with a true and unchanging success rate of 93%, which sample …