An operating manual was developed a

An operating manual was developed and provided to all investiga-
tors and coordinators for training purposes before data collection com-
menced to ensure systematic quality control. Initially, each local
coordinator reviewed the forms, checked for errors, and searched for
any missing data. Then, the local investigator performed a second re-
view to identify possible inconsistencies. Finally, the national coordina-
tors checked the database, identified possible inconsistencies, and sent
an error report to participating centers, which were required to respond
and correct all information [19].