All the data were inputted into a database set up by Epi Info 6.0 package (American Center for Disease Control and Prevention, Atlanta, GA, USA).

• 用Epi Info 6.；0软件(美国佐治亚洲亚特兰大疾病控制与预防中心，免费软件)建立数据库，数据资料经适当转化后应用社会科学统计软件包SPSS 10