Table 1.

Limits of agreement for pairwise interobserver variations in measuring QRS duration

Observers	Mean difference, ms	LL LoA, ms	95% CI	UL LoA, ms	95% CI
40 intrinsic rhythm ECGs
1 vs. 2	−10	−36	−43; −29	15	8; 23
1 vs. 3	−11	−27	−32; −22	6	1; 11
1 vs. 4	−1	−21	−27; −15	20	14; 26
1 vs. 5	−12	−29	−34; −24	6	1; 11
1 vs. 6	5	−14	−19; −9	24	18; 29
2 vs. 3	0	−30	−38; −21	29	21; 37
2 vs. 4	10	−20	−29; −12	40	31; 48
2 vs. 5	−1	−32	−41; −23	30	21; 38
2 vs. 6	15	−16	−25; −8	46	38; 55
3 vs. 4	10	−12	−18; −6	32	26; 38
3 vs. 5	−1	−19	−24; −14	17	12; 22
3 vs. 6	15	−6	−12; 0	37	31; 43
4 vs. 5	−11	−36	−43; −29	14	7; 21
4 vs. 6	5	−9	−13; −5	19	15; 23
5 vs. 6	16	−5	−11; 1	37	31; 43
Mean	2	−21	−27; −14	25	18; 31
100 biventricular paced ECGs
1 vs. 2	−7	−30	−34; −26	16	12; 20
1 vs. 3	−15	−33	−36; −30	4	0; 7
1 vs. 4	−3	−29	−33; −24	22	18; 27
1 vs. 5	−4	−24	−27; −20	15	12; 18
1 vs. 6	6	−15	−18; −11	26	23; 30
2 vs. 3	−8	−29	−33; −25	14	10; 18
2 vs. 4	4	−22	−26; −17	30	25; 34
2 vs. 5	3	−21	−26; −17	27	23; 31
2 vs. 6	13	−14	−19; −10	40	35; 45
3 vs. 4	12	−15	−20; −10	38	33; 43
3 vs. 5	10	−13	−17; −9	34	29; 38
3 vs. 6	20	−7	−12; −3	48	43; 53
4 vs. 5	−1	−28	−32; −23	25	21; 30
4 vs. 6	9	−9	−12; −6	27	24; 30
5 vs. 6	10	−13	−18; −9	34	30; 38
Mean	3	−20	−24; −16	27	22; 31

CI: confidence intervals; ECG: electrocardiogram; LL: lower limit; LoA: limits of agreement; UL: upper limit.

Limits of agreement with 95% confidence intervals for pairwise interobserver variations between the six observers measuring QRS duration in 40 intrinsic rhythm electrocardiograms with left bundle branch block (upper part of table) and 100 biventricular paced electrocardiograms (bottom part of table).