Table 1. Characteristics of subjects.

Demographic variable		Number	Effective denominator	Percentage (%)
Gender	Male	510	766	66.6
	Female	256	766	33.4
Age	≤30	229	787	29.1
	30–40	211	787	26.8
	41–50	181	787	23.0
	≥51	166	787	21.1
Education	Primary school and below	67	760	8.8
	Junior middle/special Secondary/high school education	336	760	44.2
	Junior college	142	760	18.7
	Bachelor degree or above	215	760	28.3
Occupation	Worker or peasant	208	780	26.7
	Teacher/researcher/medical Staff/civil servant	83	780	10.6
	Business/service/foreign/private Enterprise staff	144	780	18.5
	Self-employed persons	109	780	14.0
	Unemployed	81	780	10.4
	Othera	155	780	19.8

Note: The effective denominator refers to the number of respondents to the corresponding questions, excluding missing.

^a Including drivers, students, retirees and others.