Difference between Quality Assurance vs Quality Control

Let’s first look at 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.

(ref. PMBOK 5th page 227 or 255/619)

Key Takeaways:

• Both are “Prevention over inspection” and “DIRFT - Do It Right First Time” 
• Both lies the concepts of producing error free product from the start, because it’s more costly to fix an error afterwards

In layman terms:

• Quality Assurance

• is the process of laying out processes to prevent defects.
• makes sure that any process developed to produce a product is such that the product comes out of the process defect free, and conforms to all stated requirements.
• is a process based approach whose prime objective is to prevent defects in deliverables in the planning process itself to avoid the rework, which costs a lot.
• Quality audit is an example of a quality assurance process. Other examples of quality assurance are training, process definition, selection of tools, etc.
• is a proactive process, and it starts at the very beginning of the project to understand the product’s stated and non-stated requirements and expectations, and then develop the plan to meet these requirements and expectations.

• Quality Control

• is the process of measuring what we have in place to detect and repair any remaining defects.
• is a product based approach.
• is concerned with the operational activities and techniques that are used to fulfill the requirements of quality.
• functions start once the project work has begun.
• is a reactive approach and helps you find defects in deliverables.
• Inspection and product testing are a few examples of quality control tools.
• The objective of the quality control process is to make sure that the deliverables are defect free and acceptable as per the quality requirements set in the quality assurance process. If the deliverables are not found as per the requirements, a suitable corrective action will be taken.

How they relates?

Quality assurance and quality control processes are dependent on each other. The quality control process receives input from the quality assurance process, and in turn gives its feedback to the quality assurance process so that the quality assurance could validate the operational process.
For example, if the project team finds any defect during the project execution, they will correct the error and the feedback will be sent to the quality assurance team. The quality assurance people will investigate the cause of this error and they will take a corrective and/or preventive action in the process so that this error should never happen again in the future.
And once the process is updated, the quality control people will follow the process defined by the quality assurance team so that the defect does not recur.
So you see, the quality assurance process takes input from the quality control process, and the quality control process takes input from the quality assurance process.

How they differentiate against each other?

• In quality assurance, you plan to avoid the defect in the first place. On the other hand in quality control, you try to find defects and correct them while making the product.
• Quality assurance is all about prevention, and quality control is all about the detection.
• Quality assurance is a proactive process while quality control is a reactive process.
• Quality assurance is a process based approach while quality control is a product based approach.
• Quality assurance involves processes managing quality, and quality control is used to verify the quality of the product.
• Quality audit is an example of quality assurance. Inspection and testing are examples of the quality control process.
• The goal of the quality assurance process is to develop a process so that defects do not arise when you are producing the product, and quality control identifies the defects after the product is produced but is not yet released or is still in the production phase.

Case Scenario:

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.