Table 1.

The characteristics of the subjects

	Male			Female			Total
	CT group	XP group	P	CT group	XP group	P	CT group	XP group	P
Number of subjects	9790	6526		8145	9022		17 935	15 548
Mean age (SD)	58.3 (6.9)	62.0 (7.3)	<0.001	60.1 (6.6)	61.2 (7.5)	<0.001	59.1 (6.8)	61.6 (7.4)	<0.001
Age group (%)			<0.001			<0.001			<0.001
50–55	3882 (39.6)	1499 (23.0)		2372 (29.1)	2470 (27.4)		6254 (34.8)	3969 (25.5)
56–63	3355 (34.3)	1910 (29.3)		3041 (37.4)	2702 (29.9)		6396 (35.7)	4612 (29.7)
64–74	2553 (26.1)	3117 (47.7)		2732 (33.5)	3850 (42.7)		5285 (29.5)	6967 (44.8)
Smoking history (%)			<0.001			<0.001			<0.001
Never	2414 (24.7)	1962 (30.1)		7337 (90.1)	8358 (92.7)		9751 (54.4)	10 320 (66.3)
Past	1916 (19.6)	1373 (21.0)		49 (0.6)	147 (1.6)		1965 (11.0)	1520 (9.8)
Current	5213 (53.2)	2830 (43.4)		623 (7.6)	288 (3.2)		5836 (32.5)	3118 (20.1)
Unknown	247 (2.5)	361 (5.5)		136 (1.7)	229 (2.5)		383 (2.1)	590 (3.8)
Pack-years 1 (%)			<0.001			<0.001			<0.001
0	2414 (24.7)	1963 (30.1)		7338 (90.0)	8358 (92.7)		9752 (54.3)	10 321 (66.4)
0< and <30	3649 (37.2)	3097 (47.4)		504 (6.2)	298 (3.3)		4153 (23.2)	3395 (21.8)
30≤ and <50	2740 (28.0)	810 (12.4)		137 (1.7)	121 (1.3)		2877 (16.0)	931 (6.0)
50≤	735 (7.5)	284 (4.4)		29 (0.4)	12 (0.1)		764 (4.3)	296 (1.9)
Unknown	252 (2.6)	372 (5.7)		137 (1.7)	233 (2.6)		389 (2.2)	605 (3.9)
Pack-years 2 (%)			<0.001			<0.001			<0.001
0	2461 (25.1)	3345 (51.2)		7338 (90.0)	8358 (92.7)		9799 (54.6)	11 703 (75.3)
0< and <30	3602 (36.8)	1715 (26.3)		504 (6.2)	298 (3.3)		4106 (22.9)	2013 (12.9)
30≤ and <50	2740 (28.0)	810 (12.4)		137 (1.7)	121 (1.3)		2877 (16.0)	931 (6.0)
50≤	735 (7.5)	284 (4.4)		29 (0.4)	12 (0.1)		764 (4.3)	296 (1.9)
Unknown	252 (2.6)	372 (5.7)		137 (1.7)	233 (2.6)		389 (2.2)	605 (3.9)