2.2. Study populationSubject recrui

2.2. Study population

Subject recruitment: All subjects enrolled in the study lived in a community in the Haidian district. Using the community's health registration system, 260 subjects were randomly selected from a roster of potential participants identified by the community health service center. Research personnel contacted potential participants by phone, and described the study including the voluntary nature of participation in the proposed research project. After receiving detailed information, those who agreed to participate were then asked to schedule three clinical visits and interviews. Prior to the initiation of the field investigation, all participants completed a signed consent process that was approved by Institutional Review Boards at the University at Buffalo and Peking University, China.