Table 1.

Demographic characteristics of the population centres included in the study.

	Shanghaia (N = 13.5 m) %	Beijingb (N = 11.8 m) %	Wuhanb (N = 7.8 m) %	Xi'anb (N = 7.3 m) %	Guangzhoub (N = 7.3 m) %
Female	50.6	50.0	49.7	50.0	45.4
Urban	54.2	57.5	58.6	50.4	55.7
Age (years)
18-29	13.3	25.6	31.1	27.8	31.9
30-39	18.8	21.5	19.6	25.7	28.5
40-49	30.2	22.0	20.3	19.9	17.8
50-59	16.4	15.1	15.5	12.9	11.5
60-69	12.4	9.3	8.0	8.8	6.3
70-80	9.1	6.5	5.5	5.0	4.0

^aData from the fifth population census in China (2000) [43,44].

^bData from the government 1% sample survey (2005) [45-47].

m, million.