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Difference Between QA and QC.jpg

Difference between Quality Assurance and Quality Control

When opening the box containing your new circular saw, does the thought of blade misalignment occur to you? If you're anything like me, I turn into my inner alpha male who's craving the chance to saw something in half!

Without thinking, I'd line the saw up with the board and press the trigger. Imagine the potential damage and injury using a saw that failed quality tests, yet still shipped to the unknowing customer: me.

Our free market has developed such effective Quality Management Systems (QMS) that we no longer consider any possible mechanical problems related to our new purchases.

Effective QMS processes fall under the lean manufacturing umbrella and, when properly implemented, are a tremendous tool for manufacturers.

What is Quality Assurance?

Quality assurance is a process-oriented managerial tool developed to ensure quality in product development processes. QA aims to prevent defects, focusing on the process used to make the product, and it is a proactive quality process.

What is Quality Control?

Quality Control is a product-oriented corrective tool developed to identify product defects after it's assembled and before release. Quality control is a reactive process that locates and eliminates sources of quality problems using tools and equipment to prevent future defects.

Quality Assurance Audits

Quality Assurance Audits, also called QA audits, are among the most critical aspects of quality assurance in manufacturing. It consists of a series of activities carried out, ensuring that companies provide their customers with the best possible service or product. Ensuring these processes efficiently and effectively meet predetermined quality standards is the goal of quality assurance.

Quality Assurance Testing

Quality Assurance (QA) tests prevent companies from manufacturing inferior or poorly functioning products. QA is the process of monitoring a product, ensuring that no part of the finished product fails in any way. 

PDCA or Deming CycleQA follows a defined cycle referred to as the PDCA or Deming Cycle

The four phases of a Deming Cycle include:

  • Plan
  • Do
  • Check
  • Act

Although simplistic, these steps, often repeated, ensure that processes the organization developed are improved and evaluated periodically. PDCA cycles include:


Organizations should plan and establish the process-related objectives and determine the processes that are required to deliver a high-Quality end product.


Development and testing of Processes and also "do" changes in the processes


Monitoring of processes, modifying the processes, and checking whether it meets the predetermined objectives.


Implement actions that are necessary to achieve improvements in the processes

Using QA ensures the resulting component was designed and implemented using correct methods, reducing errors and problems. In the case of manufacturing, it includes testing individual pieces during the manufacturing process itself and evaluating the quality of its components. However, there are two indispensable tools for both quality assurance and quality control—machines and software.

A Coordinating Measuring Machine (CMM) measures the geometry of objects by placing sensors on different points on an object's surface using a probe. The resulting measurements confirm whether or not the part conforms to specifications.

CMM Components

CMM System ProbeCMM systems include a solid table, probes, and a spring-loaded stylus connected to a gantry. The stylus and probe rotate independently, accessing the complete area of the examined piece.

Probes use physical contact instead of lasers or optical light, relying on spherical tips comprised of rigid, stable materials. The tips mustn't be affected by weather fluctuations. Any changes in size ruin testing consistency.

There are two essential aspects of collecting information from the various points of the product. 

The purpose of collecting these points is two-fold. Individual points are used to confirm measurements of actual parts against a customer's CAD file data for the purpose of quality assurance.

Or these points can be collected to create a "point cloud," outlining the shape of the part.

This is useful when a single sample of a part is used as the foundation of a CAD program to make more parts, such as with CNC machining.

CMMs can be particularly useful when measuring points inside of holes or bores. These recessed areas can be difficult or impossible to measure with optical systems because the light tends to reflect and bounce around inside the feature, causing interference and inaccuracy.

There are several types of probes used with CMMs, including optical, laser, white light, and mechanical.

Quality Testing Software

Despite our best efforts, perfection is impossible for us humans. Nothing is perfect. However, being and realizing that we're imperfect pushes us to develop tools for us to reach near perfection.

Quality departments need a tool that interprets data from the probes to make near-flawless products. Today's testing software represents decades of experience.

Ground Rules

However, merely having sophisticated software displaying information doesn't amount to much unless there are ground rules for the testing process.

Testing shows presence of mistakes. Testing is aimed at detecting the defects within a piece of software. But no matter how thoroughly the product is tested, we can never be 100 percent sure that there are no defects. We can only use testing to reduce the number of unfound issues.

Exhaustive testing is impossible. There is no way to test all combinations of data inputs, scenarios, and preconditions within an application. For example, if a single app screen contains 10 input fields with 3 possible value options each, this means to cover all possible combinations, test engineers would need to create 59,049 (310) test scenarios. And what if the app contains 50+ of such screens? In order not to spend weeks creating millions of such less possible scenarios, it is better to focus on potentially more significant ones.

Early testing. As mentioned above, the cost of an error grows exponentially throughout the stages of the SDLC. Therefore it is important to start testing the software as soon as possible so that the detected issues are resolved and do not snowball.

Defect clustering. This principle is often referred to as an application of the Pareto Principle to software testing. This means that approximately 80 percent of all errors are usually found in only 20 percent of the system modules. Therefore, if a defect is found in a particular module of a software program, the chances are there might be other defects. That is why it makes sense to test that area of the product thoroughly.

Pesticide paradox. Running the same set of tests again and again won't help you find more issues. As soon as the detected errors are fixed, these test scenarios become useless. Therefore, it is important to review and update the tests regularly in order to adapt and potentially find more errors.

Testing is context-dependent. Depending on their purpose or industry, different applications should be tested differently. While safety could be of primary importance for a fintech product, it is less important for a corporate website. The latter, in its turn, puts an emphasis on usability and speed.

Absence-of-errors fallacy. The complete absence of errors in your product does not necessarily mean its success. No matter how much time you have spent polishing your code or improving the functionality if your product is not useful or does not meet the user expectations, it won't be adopted by the target audience.

After determining the ground rules, QA's job is continually identifying and correcting weaknesses resulting in continual improvement. 

Quality Control

Often confused with QA, quality control (QC) examines the end results. QC is essential for any company that wants to ensure that product quality is maintained and continually improved. Quality improvement is the process of analyzing the feedback received by the quality control team and workers from other aspects of the manufacturing process. Examples of quality and control activities include quality assurance audits, quality control, and quality control.

QC Benefits

Using an effective QC program provides several benefits, including

  • Increased customer loyalty
  • Gain repeat business
  • Gain new customers from referrals
  • Maintain or improve your position in the market
  • Improve safety
  • Reduce liability risks
  • Contribute to overall positive branding of your product

Ying and Yang of QC and QACosts correlating with recalls and injury settlements far exceed any profits made from the end product. The chances of a product recall or risking a customer's safety by using lousy products dramatically decrease. 

Comparing QA and QC

QA and QC are two aspects of a quality management system. Although the two processes work together, they are each defined differently. Typically, QA responsibilities cover the whole quality system. QC is a subset of QA.

What is the Difference Between QA and QC

Here's a direct comparison illustrating the differences between QA and QC.

  Quality Assurance Quality Control
Definition QA is a set of activities for ensuring quality in the processes by which products are developed. QC is a set of activities for ensuring the quality of products. The activities focus on identifying defects in the actual products produced.
Focus on QA aims to prevent defects, focusing on the process used to make the product. It is a proactive quality process. QC aims to identify (and correct) defects in the finished product. Quality control, therefore, is a reactive process.
Goal QA aims to improve development and test processes so that defects do not arise when the product is being developed. QC aims to identify defects after a product is developed and before it's released.
How Establish a good quality management system and the assessment of its adequacy. Periodic conformance audits of the operations of the system. Finding & eliminating sources of quality problems through tools & equipment, so that customers' requirements are continually met.
What Prevention of quality problems through planned and systematic activities, including documentation. The activities or techniques used to achieve and maintain the product quality, process, and service.
Responsibility Everyone on the team involved in developing the product is responsible for quality assurance. Quality control is usually the responsibility of a specific team that tests the product for defects.
Example Verification is an example of QA Validation/Software Testing is an example of QC
Statistical Techniques Statistical Tools & Techniques can be applied in both QA & QC. When they are applied to processes (process inputs & operational parameters), they are called Statistical Process Control (SPC); & it becomes part of QA. When statistical tools & techniques are applied to finished products (process outputs), they are called as Statistical Quality Control (SQC) & comes under QC.
As a tool QA is a managerial tool QC is a corrective tool
Orientation QA is process oriented QC is product oriented

In Sum

It's remarkable how we, as consumers, take product safety for granted. Statistically speaking, large product recalls are rare events. Accidents caused by failed quality management systems are more unusual still.

Comprehensive quality management systems are difficult tools to implement and require discipline for any continuous improvements. Perhaps, manufacturers aren't altruistic in their goals for QA and QC processes. Yet, we reap the benefits every time we pull the trigger for that new circular saw.




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