Table 2

Distribution and allocation of videos to investigators

Expected severity stratum	Mayo Clinic stratum								Total videos
Expected severity stratum	Normal	0	1–2	3–5	6–7	8–9	10–11	Most severe	Total videos
Core videos	5	4	6	8	8	8	6	5	50
Core videos assigned to each investigator	2^*	2	2	3	3	3	2	2	19
Duplicates of core video assigned to investigators	–	–	Each investigator was assigned two videos that duplicated two core videos from among these strata					–	2
Contact friability videos (One with CFT, one without CFT)	–	–	2	2	2	2	2	–	10
CFT videos assigned to each investigator	–	–	Each investigator was assigned two CFT pairs, where the CFT+ videos were nominally in these strata.					–	4
Total readings assigned to each investigator	2^*	2	2–4	3–5	3–5	3–5	2–4	2	25

One of the videos in the normal stratum was later found to be from a patient, thus there were truly four screening colonoscopies in this stratum.
↵* Owing to a video error in this stratum, five readers viewed one instead of two normal videos.
CFT, Contact Friability Test.