kontrollkaart

A kontrollkaart, often called a control chart in English, is a graphical tool used in statistical process control to monitor the stability of a process over time. It plots a chosen statistic—usually a mean or proportion—from samples taken at regular intervals, together with upper and lower kontrolllimits that reflect the process variability.

The purpose of a kontrollkaart is to distinguish common-cause variation, inherent in the process, from assignable-cause variation that indicates a problem. If data points stay within the limits and show no nonrandom patterns, the process is considered in control. Signals such as a point outside the limits, a run of points on one side of the center line, or a systematic trend may suggest special causes that require investigation and corrective action.

Common types include Shewhart charts for variables, such as X-bar and R or X-bar and s charts, and charts for attributes, such as p, np, c, and u charts. Data are typically collected in subgroups to estimate variability, and the_CONTROLlimits are commonly set at about ±3 standard deviations of the statistic.

Implementation involves ensuring a reliable measurement system, selecting appropriate sample sizes and sampling frequency, and interpreting patterns correctly. A kontrollkaart supports ongoing monitoring, quality improvement, and data-driven decision making about process adjustments.

The kontrollkaart concept originated with Walter A. Shewhart in the 1920s and 1930s and has become a central tool in quality management. It is widely used in manufacturing, healthcare, and service processes to maintain process stability and drive improvement.