From Ascgroup

What is the difference between Quality Control and Quality Assurance?

One of the most misunderstood concepts in Quality measurement is QC vs. QA. From a service standpoint, QC is the processes and checks put in place by a service provider (usually a contractor) to maintain service delivery levels at a predefined level. Measurement can be made at any point, including the final output, with results used to improve delivery processes. QA on the other hand, is focused solely on the output, and ideally is the measure of whether that output has achieved a predefined standard, ideally specified in some type of service level agreement (usually a contract) as a "Performance Standard" to a "Technical Requirement."

In a service contract environment, the Contractor performs the QC. A good Contractor performs QC whether required or not, though execution of a QC program is often one of the service contract requirements. Both Contractor and Customer perform QA, with the Customer doing so to "Assure" they are receiving services they pay for, while the Contractor does so to "Assure" their QC program is achieving the desired outputs.

Some Customers (for example, the US Navy) add an additional layer of Quality Measurement called Performance Assessment (PA). In this approach, the Contractor is responsible for performing both QC and QA, while the Customer performans higher level "Assessments" of overall satisfaction, with deeper inspections and targeted reviews of the Contractor's QA results if satisfaction levels are not being achieved.