Unplanned and uncontrollable variations from a planned level of performance. They may arise from external influences (e.g. abnormal weather conditions) or they may be inherent in some element of the process (e.g. slight variations in the raw materials delivered). From a quality control point of view, it is important to distinguish between a random variation and one that means that the process is going out of control. See statistical process control.
Subjects: Business and Management.