Free Certified Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers

Question 1

The primary purpose of a control chart in Statistical Process Control (SPC) is to:

Accepted Answer

Graphically distinguish between common cause and special cause variation.

Answer

Ensure the process output is always within customer specification limits.

Answer

Calculate the process capability index (Cpk) on a continuous basis.

Answer

Eliminate all sources of variation from the manufacturing process.

Question 2

A Black Belt is monitoring a process using an X-bar chart. For the last nine consecutive subgroups, the plotted averages have all fallen below the centerline. What is the most likely interpretation of this pattern?

Accepted Answer

A special cause has influenced the process, causing a sustained shift in the mean.

Answer

The process variation has significantly decreased.

Answer

The process is stable and exhibiting only common cause variation.

Answer

The measurement system is producing inaccurate readings.

Question 3

A quality manager wants to monitor the number of nonconformities (e.g., scratches, dents, paint blemishes) on the surface of refrigerators. Each refrigerator is considered one unit. The number of refrigerators inspected each hour is constant. Which of the following control charts is most appropriate for this application?

Accepted Answer

c-chart

Answer

p-chart

Answer

u-chart

Answer

np-chart

Question 4

Which of the following statements best describes the relationship between control limits and specification limits?

Accepted Answer

Control limits are calculated from process data, while specification limits are determined by customer requirements.

Answer

A process is considered capable if the control limits are wider than the specification limits.

Answer

Specification limits are always set at +/- 3 standard deviations from the process mean.

Answer

If a process is in statistical control, its output will always meet specification limits.

Question 5

A process is described as being 'in statistical control' but not 'capable'. What does this mean?

Accepted Answer

The process has too much common cause variation, preventing it from meeting customer specifications.

Answer

The process is unstable and produces an unpredictable amount of defects.

Answer

The process is affected by special causes of variation that need to be eliminated.

Answer

The measurement system is flawed, and the data cannot be trusted for capability analysis.

Question 6

In SPC, which of the following is an example of a special cause of variation?

Accepted Answer

A machine operator who is not properly trained for a specific task.

Answer

Slight, inherent vibrations in a piece of machinery during normal operation.

Answer

Minor fluctuations in ambient temperature within the facility.

Answer

The normal range of material tensile strength from a certified supplier.