Quality control

In the previous study, each subject underwent a clinical examination by two physicians, each of whom had over 3 years of experience working in a breast-surgery department. Each subject completed a questionnaire through interview by one of our trained questionnaire interviewers. At the end of each day, 10% of the questionnaires were randomly inspected to check for completeness, accuracy, and standardization. Any missing data or errors were corrected the following day. After the whole investigation was completed, the questionnaires were entered twice into a computer by two different inputters blinded to the study goals, with the second person correcting any inconsistencies found in the first set of data. Detailed information is available in the previously published paper [10].