Lean Six Sigma Black Belt Certification Control Phase: SPC 3

Question 1

Which of the following best describes the CUSUM chart's advantage over a traditional Shewhart X-bar chart?

Accepted Answer

It is more sensitive to small, sustained shifts in the process mean

Answer

CUSUM (Cumulative Sum) charts accumulate deviations from the target and are highly sensitive to small sustained shifts that Shewhart charts often miss.

Question 2

The d2 constant in control chart formulas is used to:

Accepted Answer

Estimate the process standard deviation from the average range

Answer

d2 is a control chart constant that converts the average range (R-bar) to an estimate of the process standard deviation: σ̂ = R-bar / d2.

Question 3

A short-run SPC technique is used when:

Accepted Answer

Production runs are too short to establish traditional control limits

Answer

Short-run SPC methods (e.g., standardized charts, DNOM charts) are designed for job-shop environments where each run produces too few parts for standard control limits.

Question 4

On an EWMA chart, a smaller smoothing parameter λ (lambda) results in:

Accepted Answer

Higher sensitivity to small, gradual process shifts

Answer

A smaller λ gives more weight to historical data, making the EWMA chart more sensitive to small, sustained shifts and less reactive to individual outliers.

Question 5

When a process is described as 'in statistical control,' it means:

Accepted Answer

Only common cause variation is present

Answer

Statistical control means the process exhibits only common cause (random) variation with no special causes present, not necessarily that all parts are within spec.

Lean Six Sigma Black Belt Certification Practice Test

Lean Six Sigma Black Belt Certification Practice Test

Lean Six Sigma Black Belt Certification Control Phase: SPC 3