Quality Assurance vs. Quality Control

Quality is the degree to which the inherent characteristics of a thing (i.e., your product or service) fulfill requirements and meets expectations. The process of producing something of “high quality” is commonly called “Quality Assurance.” The measurement of quality to ensure that output meets expectations is a process called “Quality Control.” When QA is based on continuous improvement and when QC precisely and accurately measures output, “high quality” is the natural result.

Quality is not grade; grade is a categorization. Software, for example, can be high quality (few defects) and low grade (few features) or low quality (many defects) and high grade (many features). Likewise, accuracy is not precision. When output is measured, a clustering of data means that the measurement is precise. Whether or not the value of that measurement is true is a matter of accuracy. An average of 30 defects per release over 9 software releases is precise but is not necessarily accurate if, for example, the people recording bugs are insufficiently trained to identify the difference between a defect and the expected output of the system.

Quality assurance is the summation of many little steps that ensure specific standards are met. On a software project, it includes things like formal code reviews, automated testing, regression system testing, and sensible coding standards. As W. Edwards Deming (one of the fathers of modern quality management) said, “You cannot expect what you inspect.” In other words, quality cannot be inspected into the product or service; it must be designed and built into the product or service. That’s quality assurance.

Quality control is a great topic for college statistic classes. It uses terms like “sampling,” “limits” and “standard deviations” and is fun in the sense that you get to create scatter diagrams and control charts. In the business world, it is challenging in the enormity of its responsibility: QC is the last safeguard against the release of a product or service that does not meet needs or expectations. It is a flashing red strobe on the ceiling of your office that lights up when the assembly line needs to be stopped and the origin of a quality problem needs to be located and addressed.

In addition to expert judgment (that’s you); the continuous output of your QC program is an input to help management identify areas in which improvements to the quality assurance program can be made. In other words, QA is about the pursuit of the perfect process: the correct combination of variables that produces a product with zero defects. At a minimum, the expectation must be that the number of defects will never exceed the control limits hard-wired to that red strobe light on the ceiling of your office. Quality control is the measuring of output (prior to reaching the customer) to ensure that standards are being met.

According to Deming, “When people and organizations focus primarily on quality, quality tends to increase and costs fall over time. However, when people and organizations focus primarily on costs, costs tend to rise and quality declines over time.”

3 Responses to “Quality Assurance vs. Quality Control”

  1. David

    Many people and organizations are confused about the difference between quality assurance (QA), quality control (QC), and testing. They are closely related, but they are different concepts. Since all three are necessary to effectively manage the risks of developing and maintaining software, it is important for software managers to understand the differences. They are defined below:
    * Quality Assurance: A set of activities designed to ensure that the development and/or maintenance process is adequate to ensure a system will meet its objectives.
    * Quality Control: A set of activities designed to evaluate a developed work product.

    Source:Difference between Quality Assurance and Quality Control


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