SPC Control Charts & Analysis 2

Question 1

Which Western Electric rule is violated when two out of three consecutive points fall beyond 2 sigma on the same side of the centerline?

Accepted Answer

Rule 2

Answer

Western Electric Rule 2 flags two out of three consecutive points beyond 2 sigma on the same side as a signal of special cause variation.

Question 2

On an X-bar chart, the Lower Control Limit (LCL) formula using the A2 constant is:

Accepted Answer

X-double-bar − A2 × R-bar

Answer

The LCL for an X-bar chart is calculated as X-double-bar minus A2 times R-bar, where R-bar is the average range.

Question 3

A p-chart is most appropriate when monitoring which type of data?

Accepted Answer

Proportion of defective items in variable-size subgroups

Answer

A p-chart monitors the proportion (fraction) of defective items and accommodates variable subgroup sizes.

Question 4

What does a steadily increasing trend of 7 or more consecutive points on a control chart indicate?

Accepted Answer

A special cause trend worth investigating

Answer

Seven or more consecutive points trending in one direction is a classic special cause signal indicating a systematic shift or drift in the process.

Question 5

Which control chart pair is used for variables data when subgroup size is 1?

Accepted Answer

Individuals and Moving Range (I-MR) chart

Answer

The Individuals and Moving Range (I-MR) chart is designed for subgroup size of n=1, where no within-subgroup range can be computed.

(SPC) Statistical Process Control Certification Practice Test