Pain conditions were assessed via a touchscreen question: “In the last month have you experienced any of the following that interfered with your usual activities.” Participants were able to select from the following categories: back pain, facial pain, headaches, knee pain, stomach/abdominal pain, hip pain, neck/shoulder pain, none of the above, prefer not to answer, or pain all over the body. If any of the pain types were selected, the participants were then asked to report whether each selected type of pain lasted for more than 3 mo. If the participants reported that they had pain all over the body, information about specific pain sites would not be recorded. Depending on their responses, individuals with more than one body site of pain lasting longer than 3 mo were considered as having MCP, those with only one body site of pain that lasted longer than 3 mo were included in the group of SCP, and those who reported no pain experienced last month were defined as PF controls. Participants with CP all over the body were excluded from our main analyses because lacking information about pain sites.