Table 1.

General characteristics of the study subjects (N = 7070)

Class	N (%)
Year of diagnosis
2000–2002	854 (12.08)
2003–2004	578 (8.18)
2005–2006	986 (13.95)
2007–2008	1168 (16.52)
2009–2010	1608 (22.74)
2011–2012	1876 (26.53)
Age (year)
<35	174 (2.46)
35–44	739 (10.45)
45–54	1801 (25.47)
55–64	2396 (33.89)
65–74	1710 (24.18)
75+	250 (3.54)
Residential area
Beijing	2597 (36.73)
Hebei	990 (14.00)
Neimenggu	576 (8.15)
Heilongjiang	516 (7.30)
Liaoning	487 (6.89)
Shandong	425 (6.01)
Shanxi	298 (4.21)
Henan	265 (3.75)
Jilin	226 (3.20)
Other	690 (9.76)