[Shewhart control charts and the cumulative sum test--the use of clinical data in quality control]

Now that quality control in health care is attracting an increasing amount of attention, every doctor needs to have knowledge and understanding of the basic principles of the most commonly used methods, especially considering that quality control starts with scrupulous monitoring of everyday procedures. The methods in use are based on statistical process control. Shewhart control charts are easy to construct and are principally suitable for the monitoring of a group of results. The cumulative sum test is more suitable for a continuous process control, even of smaller quantities. These methods primarily give a warning signal, with a request for further analysis, rather than giving direct evidence of poor quality.