“…In the future, to monitor ongoing data on the basis of stabilized processes for every surgeon, three goals must be reached: first, a continuous and iterative evaluation must be performed (phase I); second, small process improvements or deteriorations must be detected using cumulative sum and exponentially weighted moving average charts (phase II) [19], and the duration of the learning period must be measured scientifically if there is an improvement [1]; finally, when making comparisons, data from all levels of the health care process (rational group), such as physicians, wards, shifts and the like, should be routinely collected into the database for the SPC system to enable comparisons, such as the comparisons of group A to E in this study. These group selections must be such that random variations are included within a group so that assignable or special causes between groups can be identified [20].…”