Certified Six Sigma Black Belt Exam Certified Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers 3

Question 1

A Black Belt is setting up a control chart for a process where individual measurements follow a non-normal distribution. Which approach is most appropriate?

Accepted Answer

Transform the data to achieve approximate normality before charting

Answer

Use standard X-bar and R chart limits regardless of distribution

Answer

Increase the sample size to 50 to force normality

Answer

Use attribute charts instead of variables charts

Question 2

What is the primary purpose of rational subgrouping in SPC?

Accepted Answer

To minimize the variation within subgroups so that between-subgroup variation represents assignable causes

Answer

To ensure each subgroup is as large as possible for statistical power

Answer

To maximize the variation within subgroups and minimize variation between subgroups

Answer

To randomly assign measurements to subgroups regardless of time or conditions

Question 3

A process is monitored using a p chart with variable subgroup sizes. The control limits appear as a staircase pattern. What causes this?

Accepted Answer

Different subgroup sizes produce different standard error values, resulting in different control limit widths

Answer

The process proportion defective is changing over time

Answer

The attribute data should be monitored on a c chart instead

Answer

The center line was incorrectly calculated

Question 4

Which of the following is a key assumption for calculating a valid Cpk index?

Accepted Answer

The data must come from a process that is in statistical control

Answer

The specification limits must be symmetrical about the target

Answer

The sample size must be at least 100

Answer

The process must be operating at less than 1% defective

Question 5

A CUSUM chart signals an out-of-control condition. Compared to a Shewhart chart, what type of process shift is the CUSUM chart most effective at detecting?

Accepted Answer

Small persistent shifts of 0.5 to 2 sigma

Answer

Large sudden shifts of 3 sigma or more

Answer

Cyclic patterns in the data

Answer

Outliers caused by measurement error

Question 6

When constructing an X-bar and S chart instead of an X-bar and R chart, what is the primary reason for choosing the S chart?

Accepted Answer

The S chart is more accurate when subgroup sizes are large, typically greater than 8 or 10

Answer

The S chart is easier to calculate by hand

Answer

The S chart can detect non-normal data more effectively

Answer

The R chart cannot be used with variable subgroup sizes