FREE Lean Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers

Question 1

A quality team is monitoring the number of nonconforming units produced on an assembly line.
Each hour, they inspect a different number of units based on production volume.
Which type of control chart is most appropriate for monitoring the proportion of nonconforming units in this scenario?

Accepted Answer

p-chart

Answer

np-chart

Answer

c-chart

Answer

I-MR chart

Question 2

Which of the following statements most accurately describes the fundamental difference between control limits and specification limits?

Accepted Answer

Control limits represent the voice of the process, while specification limits represent the voice of the customer.

Answer

Control limits are set by management, while specification limits are calculated from process data.

Answer

Specification limits are used for attribute data, while control limits are used for variable data.

Answer

Control limits are wider than specification limits to allow for normal process variation.

Question 3

An operator running a stable process notices a measurement that is slightly above the process average but still well within the control limits. To be proactive, the operator makes a small adjustment to the machine settings to bring the next output closer to the average. What is the most likely result of this type of action over time?

Accepted Answer

An increase in overall process variation.

Answer

A gradual reduction in process variation.

Answer

The process mean will shift significantly lower.

Answer

No significant change in the process output.

Question 4

A process control plan requires taking a sample of five consecutive parts from a machine every hour to form a subgroup for an Xbar-R chart. What is the primary principle behind this sampling strategy, known as rational subgrouping?

Accepted Answer

To minimize within-subgroup variation and maximize the opportunity to see variation between subgroups.

Answer

To capture the maximum amount of variation within each subgroup.

Answer

To ensure that special cause variation is included within each subgroup.

Answer

To simplify data collection by spreading it evenly across a shift.

Question 5

An analysis of a manufacturing process shows that its output is highly predictable and exhibits only common cause variation. However, a process capability study (Cpk) reveals a value of 0.75. Which of the following best describes this process?

Accepted Answer

In control but not capable.

Answer

Capable but not in control.

Answer

In control and capable.

Answer

Out of control and not capable.

Question 6

When interpreting a control chart, which of the following is the most direct and universally recognized signal of a special cause of variation?

Accepted Answer

A single point falling outside the upper or lower control limits.

Answer

Seven consecutive points trending in one direction.

Answer

Fourteen points in a row alternating up and down.

Answer

Two out of three consecutive points in Zone A on the same side of the centerline.