Fundamentals Flashcards

Which of the following best describes 'common cause variation' in a process?

Answer: Variation inherent to the process that is always present

Common cause variation is the natural, inherent variability in a process that is always present and results from many small, everyday factors.

On an X-bar chart, what does a single point beyond the upper or lower control limit indicate?

Answer: A potential special cause that should be investigated

A point beyond a control limit is a signal of special cause variation that warrants immediate investigation.

What is the primary purpose of a process capability index (Cp)?

Answer: To compare the process spread to the specification width

Cp compares the specification width (USL − LSL) to the process spread (6σ) to indicate whether the process can fit within specifications.

A rational subgroup in SPC is best defined as a group of measurements that:

Answer: Minimizes the chance of special causes occurring within the group

Rational subgroups are sampled so that variation within the group reflects only common causes, making between-group variation a reliable signal of process changes.

Which control chart is most appropriate for monitoring the number of defects per unit when the subgroup size varies?

Answer: u chart

The u chart monitors the average number of defects per unit and accommodates varying subgroup sizes.

In SPC, 'control limits' are typically set at:

Answer: ±3 sigma from the process mean

Control limits are conventionally placed at ±3 sigma from the process mean, providing a 99.73% probability that in-control points fall within them.

When a control chart shows 8 consecutive points on the same side of the center line, this is an example of:

Answer: A run rule signaling a potential process shift

Eight or more consecutive points on one side of the center line is a run rule that signals a potential process mean shift.