Quality control versus quality assurance in sourcing

This article describes common industry practice, not official rules.

Quality control checks the goods. Quality assurance checks how the factory prevents problems from happening in the first place. Buyers often meet these terms together when they source from factories in China. They overlap, but they answer different questions.

What quality control covers

Quality control looks at the product and the batch in front of the buyer. Common activities include:

• checking incoming materials against the specification and the approved sample
• checks during production, often called in-process checks
• final inspection of finished goods before packing
• third-party inspection of an order

A third party that is not the factory or the seller can carry out the last activity. The inspector samples the lot, checks the goods against the inspection checklist, and writes an inspection report.

Laboratory testing is a separate activity. A laboratory measures properties under controlled conditions and produces a test report. That report describes what was measured. It is not the same as a factory inspection.

What quality assurance covers

Quality assurance looks at the system behind the product. A buyer usually asks about:

• documented processes, such as how a line is set up and how a change is approved
• training for the people who run the line and do the checks
• control of sub-suppliers and materials, so the factory knows what it buys and from whom
• records of checks, test results and changes
• corrective action, meaning what the factory does after a defect is found and whether the cause is removed
• factory audits, which review these points on site

An audit shows how the system looked on the day of the visit. It does not show the goods that will ship later.

Where each sits in sourcing

Stage	Usual focus
Specification and approved sample	Agree what good looks like: the technical drawing, bill of materials, artwork and approved sample
Supplier audit	Quality assurance: how the factory controls processes, records and sub-suppliers
Pre-production inspection	Quality control on materials and samples before bulk production starts
During production inspection	Quality control while the order is being made
Pre-shipment inspection and container loading check	Quality control on finished goods and on the loading of the container
After a failed inspection	Re-inspection, rework and corrective action; quality assurance checks whether the cause has been removed

The stages do not follow one fixed pattern. A supplier audit commonly comes before the purchase order. The inspection stages usually follow the order. When the product or the factory is new to the buyer, a buyer may add stages or make them larger, as set in the contract.

Why buyers commonly combine them

Quality control finds problems that already exist in the goods. Quality assurance gives a reason to expect later goods to be made the same way. A buyer who relies only on final inspection sees the problem after the goods are made. A buyer who relies only on the factory's system has no direct check on the lot in hand. Using them together lets each cover the gap in the other.

What to ask the supplier about each

For quality control:

• How are incoming materials checked before use, and against which document?
• Where in the line are checks made, and who records them?
• How are defective units separated and reworked?
• How is the sample for the final check chosen?

For quality assurance:

• Which processes are written down, and who approves changes?
• How are operators trained, and how is that training recorded?
• Which sub-suppliers supply materials, and how are they checked?
• What happens after a defect is reported, and how is the cause closed?
• Can the factory share records from earlier corrective actions?

Legal and certification questions

Whether a legal or certification requirement applies is for the regulator or an accredited laboratory to confirm.