[Control charts--a useful graphical tool for the analysis of process variation over time].

Most hospital work can be seen as linked processes. Designed to examine process performance, control charts allow distinction between two types of variation. While processes that exhibit special cause variation are unstable and should be improved by eliminating special causes, processes exhibiting only common cause variation are predictable and should be improved by fundamental redesign. Control charts are also key tools to monitor such intended changes. This paper provides an overview of the most common types of control charts and the most important interpretation rules.