SPC Fundamentals 4

Question 1

The Western Electric (WECO) rules are used in SPC to:

Accepted Answer

Detect non-random patterns in control chart data

Answer

WECO rules are a set of pattern-recognition tests applied to control charts to detect special causes beyond simple out-of-limit points.

Question 2

What is 'over-adjustment' (also called tampering) in the context of SPC?

Accepted Answer

Making process adjustments in response to common cause variation

Answer

Tampering occurs when operators make unnecessary adjustments to a process reacting to common cause variation, which actually increases overall variation.

Question 3

For an X-bar and R chart, after how many subgroups are the control limits considered reliable estimates?

Accepted Answer

20–25 subgroups

Answer

A minimum of 20–25 subgroups is generally recommended to establish stable and reliable control limits.

Question 4

In a p-chart, what does the plotted statistic represent?

Accepted Answer

The proportion of defective items in a subgroup

Answer

The p-chart plots the proportion (fraction) of nonconforming items in each subgroup.

Question 5

Which measure of central tendency is plotted on the center line of a standard X-bar chart?

Accepted Answer

The grand average of subgroup means

Answer

The center line of an X-bar chart is the grand mean (X-double-bar), calculated as the average of all subgroup averages.

(SPC) Statistical Process Control Certification Practice Test

(SPC) Statistical Process Control Certification Practice Test

SPC Fundamentals 4