Several books are available that describe how to construct control charts. Unfortunately none of these books show how to adjust control charts for the severity of the patients' illness. Without such adjustments control charts not only loose face validity but could lead to wrong conclusions. In this article we provide a step-by-step guide regarding how to control for changes in patients' severity of illness across time periods. We illustrate the use of the approach in examining falls in nursing homes. A control chart was constructed to compare observed falls to the residents' risk of fall measured on admission. Analysis led to conclusions radically different from an unadjusted chart.