Data collection
All study data will be obtained from clinical records and will be electronically entered by the local principal and sub-investigators at each participating site where the data originated, using a validated web-based system. Data integrity will be enforced through appropriate range checks and consistency checks at the time of data entry, before the data are committed to the database. Additional errors will be detected by programs designed to detect missing data or specific errors in the stored data. These errors will be summarized along with detailed descriptions for each specific problem in a data query report, which will be sent to the principal investigator of each site. Data entered into the database will be retrievable for viewing through the data entry application. The audit trail will register all the activities performed by the authorized operators. The type of activity that an individual user may undertake is regulated by the privileges associated with his/her user identification code and password. A complete back up of the primary database will be performed once a week and stored indefinitely on a twin server. Incremental data back-ups will be performed on a daily basis and retained for at least 1 week on-site.There was no structured plan to promote participant retention.