Demographic characteristics of residents in Shenzhen and Xiuning in China in 2007.

*Median age and household size between urban and rural groups were compared by the Wilcoxon rank sum test, Z = 12.137, P<0.001 and Z = −13.664, P<0.001.
‡Frequencies for male, age group, highest level of education, occupation status, household with children <5 years and household with children <15 years between urban and rural group were compared by the Chi-squared test, with p = 0.747, p<0.001, p<0.001, p<0.001, p = 0.016 and p = 0.013, respectively.