Table 2

Interobserver agreement at the primary reader level

Characteristic		Frequency of characteristic, n/N (%)*	Overall observed agreement, (%)†	Unadjusted kappa	95% CI	Adjusted kappa‡
Uninterpretable§		28/9723 (0.3)	0.98	0.25	0.23 to 0.27	0.97
	Rotated	2/21 (9.5)	0.86	0.49	0.07 to 0.91	0.71
	Blurry	7/21 (33.3)	0.76	0.52	0.09 to 0.95	0.52
	Over penetrated	0/21 (0)	0.95	0.00	0 to 0	0.90
	Under penetrated	3/21 (14.3)	0.90	0.69	0.26 to 1.12	0.81
	Clipped image	5/21 (23.8)	0.95	0.88	0.45 to 1.3	0.90
Any PEP¶		959/9533 (10.1)	0.79	0.35	0.33 to 0.37	0.57
	Air bronchogram**	14/692 (2.0)	0.87	0.18	0.10 to 0.25	0.75
	Silhouette sign**	360/692 (52.0)	0.72	0.39	0.31 to 0.46	0.45
	Size criteria**	361/692 (52.2)	0.65	0.16	0.09 to 0.24	0.29
	Pleural effusion	45/959 (4.7)	1.00	1.00	0.94 to 1.06	1.00
	Aged 3–11 months	492/4990 (9.9)	0.79	0.36	0.33 to 0.38	0.58
	Aged 12–23 months	311/3016 (10.3)	0.78	0.34	0.30 to 0.37	0.55
	Aged 24–35 months	156/1527 (10.2)	0.79	0.35	0.30 to 0.40	0.57
Right-sided PEP only		480/9533 (5.0)	0.83	0.28	0.26 to 0.30	0.66
Left-sided pleural pneumonia only		120/9533 (1.3)	0.94	0.27	0.25 to 0.29	0.88
Bilateral PEP (both)		58/9533 (0.6)	0.96	0.21	0.19 to 0.23	0.92
Bilateral PEP (any)		269/9533 (2.8)	0.81	0.12	0.10 to 0.14	0.62

*Both primary readers agreed to the presence of characteristic. Discordant interpretations were assumed to not have the characteristic.
†Both primary readers agreed to either the presence or absence of the characteristic.
‡Prevalence-adjusted, bias-adjusted kappa statistic.
§7 Uninterpretable images are missing data on image characteristics.
¶190 of 9723 images were classified as by either primary reader as uninterpretable and were excluded.
**267 of the 959 images classified by primary readers as PEP are missing data on image features.
PEP, primary endpoint pneumonia.