Results
After random selection, 50 chart numbers were identified in each cohort. Retrieval of charts based on chart number lead to the exclusion of 2 from the 2006 cohort and 4 from the 2009. These charts were excluded because they could not be retrieved from the archives at the time of the chart review. They had been requested elsewhere and no tracking system existed at that time. From the 2006 and 2009 cohorts 48 and 46 distinct charts were kept for the study.