Statistics Quality Control & Assurance 5

Question 1

In statistical process control, the term 'rational subgroup' refers to subgroups that:

Accepted Answer

Are formed so that variation within a subgroup reflects only common causes, maximizing the chance of detecting special causes between subgroups

Answer

Rational subgroups are collected to capture short-term, within-subgroup common-cause variation so that between-subgroup differences reveal special causes.

Question 2

A CUSUM (Cumulative Sum) control chart is preferred over a Shewhart X-bar chart when the goal is to:

Accepted Answer

Detect small, sustained shifts in the process mean more efficiently

Answer

CUSUM charts accumulate deviations from the target and are especially sensitive to small, persistent shifts (1-2 sigma) that Shewhart charts may miss for many samples.

Question 3

The Lower Control Limit (LCL) for an R-chart is sometimes set to zero. This occurs because:

Accepted Answer

Negative ranges are physically impossible, and the calculated LCL formula can yield a negative value for small subgroup sizes

Answer

For small subgroup sizes (typically n ≤ 6), the D3 constant used in the LCL formula equals zero, so the calculated LCL is set to 0 since a range cannot be negative.

Question 4

In Design of Experiments (DOE) applied to quality improvement, a '2^k factorial design' refers to an experiment with:

Accepted Answer

k factors each tested at exactly two levels

Answer

A 2^k factorial design tests k factors, each at two levels (high and low), resulting in 2^k total treatment combinations when fully replicated.

Question 5

Poka-yoke (mistake-proofing) devices in quality assurance are intended to:

Accepted Answer

Prevent defects from occurring or detect them immediately at the source

Answer

Poka-yoke devices physically prevent errors from occurring or provide immediate detection/feedback so defects cannot be passed to the next stage.

Statistics Practice Test

Statistics Practice Test

Statistics Quality Control & Assurance 5