2. Retrospective data collection To ensure optimal quality, all data collected retrospectively by chart review will be entered electronically by clinical research nurses using a personal identification code and password-protected web-based data collection system. The clinical research nurses will receive formal training in the methods of data abstraction and recording. An operation manual that includes definitions and acceptable data sources for all variables will be distributed. Reliability of data abstraction will be assessed by randomly selecting 30 cases for independent collection by the two study nurses.