Quality, variation, defects, and customer value

Learning objectives

• Define variation and defect in operational terms.
• Distinguish specification from actual process performance.
• Link CTQs to customer value for garment products.

Quality is consistency to requirement

Outputs vary because inputs and processes vary. A defect occurs when an output fails a requirement that matters to the customer. Common-cause variation belongs to the system; special-cause variation reflects an identifiable change. Prevention is stronger than sorting.

Centre and spread

• The mean tells you where the process sits.
• The standard deviation tells you how wide it swings.
• Both must be inside tolerance to be capable.

Garment-factory example

Chest measurements may average correctly while individual garments spread outside tolerance. The average alone hides the risk; both centre and spread must be controlled.

Method

1. Identify the customer requirement and operational definition.
2. Define the unit and what counts as a defect.
3. Measure the distribution — centre and spread.
4. Separate common and special causes and remove causes at source.

Common mistakes

• Using averages without also reporting spread.
• Calling every deviation an operator error.