Glossary
Apply statistical process control (SPC)

Random cause

A variation is due to random causes if it is caused by a large number of small variations in the many parameters controlling the process.

Assignable cause

When a deviation is not due to a random cause, it is said to be due to an assignable cause. By analysis, we can identify (assign) the parameter which is at the origin of this process maladjustment, and the deviation of the parameter must be corrected.