Question

Identify three specific criteria for determining when a process is out of statistical control.

Short answer

When a statistical process shows one of the following features, then it is said to be out of control:

• There is a distinguishably visible pattern, trend, or cycle.
• At least one point exceeds the upper control limit, and at least one point falls below the lower control limit.
• The points follow the Run of 8 Rule, which states that there must be at least eight points above or below the centerline in a row.

Step-by-step solution

Given information

The conditions for identifying when a statistical process is out of control are to be determined.

Criteria of determining when the statistical process is out of control

If a statistical process possesses one of the following characteristics, then it is said to be unstable or out of control:

• There is a clearly identifiablepattern, trend, or cycle which is not of random nature.
• At least one point is above the upper control limit(UCL),and at least one point falls below the lower control limit (LCL).
• The points depict the Run of 8 Rule, which can be determined as that eight or more consecutive points above or below the centerline.