1. Acquiring Proficiency in Off-Pump Surgery: Traversing the Learning Curve, Reproducibility, and Quality Control 
Gavin J. Murphy, MD, Chris A. Rogers, PhD, Massimo Caputo, MD, Gianni D. Angelini, MD 
The Annals of Thoracic Surgery 
Volume 80, Issue 5, Pages (November 2005)
DOI: /j.athoracsur
Copyright © 2005 The Society of Thoracic Surgeons Terms and Conditions

2. Fig 1
Cumulative failure charts (left) and cumulative observed minus expected failure charts (right) surgical failure after off-pump coronary artery bypass grafting for the same data set. The data represents the performance of a single resident and a consultant trainer. To define whether changes in performance remain within or exceed acceptable limits, control boundaries are calculated by defining the acceptable failure rate, the unacceptable failure rate, the α value (ie, the probability of concluding that the failure rate has increased when, in fact, it has not [type I error]), and the β value (ie, the probability of concluding that the failure rate has not increased when, in fact, it has [type II error]). If the graph of cumulative failures crosses the upper boundary, then we conclude that the failure rate has increased to the unacceptable rate and action should be taken. If it crosses the lower boundary, we conclude that the failure rate is equal to or below the acceptable rate. (Light-face broken lines = consultant, on-pump; light-face solid line = consultant, off pump; bold broken lines = resident, on-pump; bold solid line = resident, off-pump.)
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2005 The Society of Thoracic Surgeons Terms and Conditions

3. Fig 2
Sequential probability ratio test (SPRT) (left) and variable life-adjusted display (VLAD) (right) charts for a single resident compared with the consultant (data for the consultant’s 200 most recent operations within the study period are shown for comparison on each chart). The “X” axis represents operation number, not calendar time. Note that the “Y” axis is different for VLAD plots (cumulative observed–predicted risk of failure) and SPRT plots (cumulative log likelihood ratio), and the charts have been scaled accordingly. The SPRT chart graphs the cumulative log likelihood statistic and in contrast to the cumulative failures chart has boundary lines drawn horizontally rather than at an angle. The graph starts at zero and is incremented by 1-si for a failure and decremented by si for a success, in which si is defined by the predicted risk of failure for operation (p0i) and the increase in failure rate (risk) that the chart is designed to detect (for description, see reference 34). Acceptable performance in a VLAD plot should oscillate around zero, whereas acceptable performance in an SPRT plot will tend toward the “accept” boundary line. (Light-face solid line = consultant; bold solid line = resident; bold broken lines = boundary lines; broken line with 2 center dots = expected failures.)
The Annals of Thoracic Surgery  , DOI: ( /j.athoracsur )
Copyright © 2005 The Society of Thoracic Surgeons Terms and Conditions