Quality Control and Quality Assurance

How to recognize a control practice from an assurance practice?

Quality means meeting requirements and meeting customer needs, which means a defect-free product from both the producer’s and the customer’s viewpoint. Both quality control and quality assurance are used to make quality happen. Of the two, quality assurance is the more important.

Quality Assurance (QA) is associated with a process. Once processes are consistent, they can "assure" that the same level of quality will be incorporated into each product produced by that process.

QC is an activity that verifies whether or not the product produced meets standards.
QA is an activity that establishes and evaluates the processes that produce the products.

If there is no process, there is no role for QA. Assurance would determine the need for, and acquire or help install system development methodology, estimation processes, system maintenance processes, and so forth.
Once installed, QA would measure them to find weaknesses in the process and then correct those weaknesses to continually improve the processes.

It is possible to have quality control without quality assurance.

The following statements help differentiate QC from QA

QC relates to a specific product or service.
QC verifies whether particular attributes exist, or do not exist, in a specific product or service.
QC identifies defects for the primary purpose of correcting defects.
QC is the responsibility of the worker.

QA helps establish processes.
QA sets up measurement programs to evaluate processes.
QA identifies weaknesses in processes and improves them.
QA is a management responsibility, frequently performed by a staff function.
QA evaluates whether or not quality control is working for the primary purpose of determining whether or not there is a weakness in the process.
QA is concerned with all of the products that will ever be produced by a process.
QA is sometimes called quality control over quality control because it evaluates whether quality control is working.
QA personnel should not ever perform quality control unless doing it to validate quality control is working.