Kontrollkriteriet

Kontrollkriteriet, translated as the control criterion, is a term used in quality control and statistical process control to denote the predefined standards that determine whether a process or measurement is in control or requires corrective action. It specifies threshold values, patterns, or behaviors that indicate stability or instability and guides decisions about monitoring, adjustment, and process capability.

In control charts, the control criterion includes events such as data points outside control limits, runs of consecutive points on one side, trends, or cycles. The exact specification depends on the method and domain; practitioners may emphasize limits, run rules, or both. The criterion is chosen to balance sensitivity and specificity: overly lax criteria may miss problems, while overly strict criteria may trigger unnecessary changes.

Kontrollkriteriet is used in manufacturing, service processes, and environmental monitoring to maintain consistency and detect deviations early. It is linked to concepts such as common-cause and special-cause variation and to decision rules for intervention.

Examples: With control limits set at ±3 standard deviations on a Shewhart chart, a single point beyond the limits may meet the criterion; additional rules (for example, seven points in a row above the center line) extend the criterion for judging out-of-control conditions.

See also: Statistical process control, control chart, process capability, quality management.