Table 2.

Sum scores divided in: correct (compliance with quality criteria), errors (no compliance with quality criteria) and stability (same quality in both radiographic series per clinic) in assessments for all clinics. Mean (95% CI) and presented in percentile (p) groups with a proposed grading: A-E

	Mean	95% conf. interval	Min	p10	p25	Median	p75	p90	Max
Correctd Proposed scoringa				E	D	C	B	A
All projections	33.56	(32.69 34.43)	14	25	31	34	37	40	43
AP/PA	15.26	(14.88 15.65)	7	12	14	16	17	18	18
L1-L4	9.45	(9.11 9.78)	3	7	8	9	11	12	14
L5/S1	8.85	(8.50 9.21)	2	6	8	9	10	12	12
Errorc Proposed scoringa				A	B	C	D	E
All projections	10.42	(9.55 11.29)	1	4	7	10	13	19	30
AP/PA	2.72	(2.34 3.10)	0	0	1	2	4	6	11
L1-L4	4.55	(4.22 4.89)	0	2	3	5	6	7	11
L5/S1	3.14	(2.79 3.50)	0	0	2	3	4	6	10
Stabilityb Proposed scoringa				E	D	C	B	A
All projections	5.20	(4.72 5.68)	0	2	3	5	7	9	14
AP/PA	1.96	(1.70 2.21)	0	0	1	2	3	4	6
L1-L4	1.76	(1.56 1.95)	0	0	1	2	2	3	5
L5/S1	1.49	(1.28 1.69)	0	0	0	1	2	3	5

^aProposed cut point in grading A-E. Only used for the “all projections” group. A = highest grade

^bStability in quality measured as whether the two assessed radiographic series had the same scoring (ok versus error)

^cSum of errors in all assessments. ^d Sum of correct assessments. Classified in grades according to mean +/− SD criteria, see Materials and methods section