Many people have trouble understanding the difference between Quality Assurance (QA) and Quality Control (QC) as they are preparing for their PMP Exam. That is not surprising. The terms are very closely related and if you don’t work in the field, the difference doesn’t seem too obvious.
Let’s first look at the PMBOK Guide definition for each:
Perform Quality Assurance: The process of auditing the quality requirements and the results from quality control measurements to ensure appropriate quality standards and operational definitions are used.
Perform Quality Control: The process of monitoring and recording results of executing the quality activities to assess performance and recommend necessary changes.
As always, the PMBOK Guide is a bit dry in it’s definitions, but before we “translate” these definitions into everyday words, it is a good idea to remind ourselves first of two other quality concepts. They are “Prevention over inspection” and “DIRFT - Do It Right the First Time”. At the heart of these two concepts lies the idea that everything we produce should be produced error free from the start, because it’s more costly to fix an error afterwards.
So... how can we assure that our deliverables are produced error free? Simple: We have to put appropriate processes in place; processes that are aimed at helping us produce these deliverables without errors every time. But because there will always be some deviation from even the best processes, we also have to put some controls in place, which measure the results after the fact, so that we can make adjustments if necessary.
Quality Assurance are therefore the processes that are aimed at preventing any defects and Quality Control are the measurements we have in place to detect and repair any remaining defects.
So let’s assume that you are manufacturing the iPhone. In QA you put all the processes in place to ensure that each iPhone is manufactured defect free. This would include the types of manufacturing equipment used, training people and documenting all production processes. QC comes into play after the fact by testing the finished product. For instance you do a sample testing to see if a randomly picked iPhone from your production line passes or fails the standards.