Table 3

Test performance: need for patient surveillance

	Histology interval (reference standard)
	High risk: 1 year	Intermediate risk: 3 years	Low risk: 5 years	Low risk: no surveillance	No adenoma: no surveillance	Total
NBI colonoscopy interval
High risk: 1 year	(a) 9	4	0	(b′) 3	(b) 2	18
Intermediate risk: 3 years	3	30	12	10	2	57
Low risk: 5 years	2	13	46	52	13	126
Low risk: no surveillance	(c′) 0	4	9	(d′) 100	19	132
No adenoma: no surveillance	(c) 0	4	27	28	(d) 107	166
Total	14	55	94	193	143	(N) 499

Adenoma present (solid line partitions)
Test sensitivity=sum of cells in box (a)/sum of cells in boxes (a)+(c)=297/356=83.4%.
Test specificity=sum of cells in box (d)/sum of cells in boxes (d)+(b)=107/143=74.8%.
Error rate=(b+c)/N=95/499=19.0%.
Surveillance required (dashed line partitions)
Test sensitivity=sum of cells in box (a)/sum of cells in boxes (a)+(c′)=119/163=73.0%.
Test specificity=sum of cells in box (d′)/sum of cells in boxes (d′)+(b′)=254/336=75.6%.
Exact matching=sum of cells with matching surveillance interval / N=339/499=67.9%.
Conservative matching=sum of cells with matching or over surveillance/N=437/499=87.6%.
Error rate=(b′+c′)/N=126/499=25.2%.
NBI, narrow band imaging.