Chapter 6 - Statistical Quality Control

Statistical quality control (SQC)

Category of statistical tools used to evaluate organizational quality.

Descriptive statistics

Used to describe quality characteristics and relationships.

Statistical process control (SPC)

Uses samples and control charts to determine if a process is in control.

Acceptance sampling

Randomly inspecting a sample to accept or reject the entire lot.

Common causes of variation

Random variation that is inherent in a process and not easily identified.

Assignable causes of variation

Identifiable variation due to specific causes that can be corrected.

Mean (average)

A measure of central tendency of a data set.

Range

The difference between the largest and smallest values in a data set.

Standard deviation

A measure of how spread out the numbers in a data set are from the mean.

Out-of-control

A condition where one or more data points fall outside the control limits.

Variable

A measurable product characteristic that can have a range of numeric values.

Attribute

A countable product characteristic (e.g., number of defects).

Process capability

The ability of a process to consistently produce output within specification limits.

Product specifications

Acceptable upper and lower limits of a quality characteristic.

Process capability index (Cp, Cpk)

A statistical measure of how well a process is performing within specifications.

Six Sigma quality

A high standard of quality aiming for no more than 3.4 defects per million opportunities.

Control chart

A graph used in SPC to study how a process changes over time.

X-bar chart

A control chart used to monitor changes in the mean of a process.

R-chart

A control chart used to monitor the range (variability) of a process.

P-chart

A control chart used to monitor the proportion of defective items in a process.

C-chart

A control chart used to monitor the number of defects in a single unit.

DMAIC

Define, Measure, Analyze, Improve, Control — a Six Sigma problem-solving process.