Quality control [QC] is a procedure or set of procedures intended to ensure that a manufactured product or performed service adheres to a defined set of quality criteria or meets the requirements of the client or customer. QC is similar to, but not identical with, quality assurance [QA]. While QA refers to the confirmation that specified requirements have been met by a product or service, QC refers to the actual inspection of these elements.
QA is sometimes expressed together with QC as a single expression: quality assurance and control [QA/QC].
The quality control procedure
In order to implement an effective QC program, an enterprise must first decide which specific standards the product or service must meet. Then the extent of QC actions must be determined -- for example, the percentage of units to be tested from each lot.
Next, real-world data must be collected -- such as the percentage of units that fail -- and the results reported to management personnel. After this, corrective action must be decided upon and taken. For example, defective units must be repaired or rejected, and poor service repeated at no charge until the customer is satisfied. If too many unit failures or instances of poor service occur, a plan must be devised to improve the production or service process; then that plan must be put into action.
Finally, the QC process must be ongoing to ensure that remedial efforts, if required, have produced satisfactory results and to immediately detect recurrences or new instances of trouble.
See also: Total Quality Management
This was last updated in December 2019
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Figure 1: Quality System, Quality Assurance, and Quality Control Relationships
Quality Assurance
Quality assurance can be defined as "part of quality management focused on providing confidence that quality requirements will be fulfilled." The confidence provided by quality assurance is twofold—internally to management and externally to customers, government agencies, regulators, certifiers, and third parties. An alternate definition is "all the planned and systematic activities implemented within the quality system that can be demonstrated to provide confidence that a product or service will fulfill requirements for quality."
Quality Control
Quality control can be defined as "part of quality management focused on fulfilling quality requirements." While quality assurance relates to how a process is performed or how a product is made, quality control is more the inspection aspect of quality management. An alternate definition is "the operational techniques and activities used to fulfill requirements for quality."
Industry Perspectives on QA and QC
For some service organizations, the concept of quality control may be foreign because there is no tangible product to inspect and control. The quality assurance function in a service organization may not include quality control of the service but may include quality control of any products involved in providing the service.
A service may include products that are documents [such as a report, contract, or design] or tangible products [such as a rental car or units of blood]. It may be necessary to control product quality in a service organization to ensure that the service meets customer requirements.
QA, QC, and Inspection
Inspection is the process of measuring, examining, and testing to gauge one or more characteristics of a product or service and the comparison of these with specified requirements to determine conformity. Products, processes, and various other results can be inspected to make sure that the object coming off a production line, or the service being provided, is correct and meets specifications.
Quality Assurance and Audit Functions
Auditing is part of the quality assurance function. It is important to ensure quality because it is used to compare actual conditions with requirements and to report those results to management.
In The Quality Audit: A Management Evaluation Tool [McGraw-Hill, 1988], Charles Mill wrote that auditing and inspection are not interchangeable: “The auditor may use inspection techniques as an evaluation tool, but the audit should not be involved in carrying out any verification activities leading to the actual acceptance or rejection of a product or service. An audit should be involved with the evaluation of the process and controls covering the production and verification activities.”
Formal management systems have evolved to direct and control organizations. There are quality management systems [QMSs] as well as environmental or other management systems, and each of these systems may be audited.
History of QA and QC
Quality has been defined as fitness for use, conformance to requirements, and the pursuit of excellence. Even though the concept of quality has existed from early times, the study and definition of quality have been given prominence only in the last century.
1920s: Quality Control
Following the Industrial Revolution and the rise of mass production, it became important to better define and control the quality of products. Originally, the goal of quality was to ensure that engineering requirements were met in final products. Later, as manufacturing processes became more complex, quality developed into a discipline for controlling process variation as a means of producing quality products.
1950s: Quality Assurance and Auditing
The quality profession expanded to include the quality assurance and quality audit functions. The drivers of independent verification of quality were primarily industries in which public health and safety were paramount.
QA and QC Resources
You can also search articles, case studies, and publications for quality assurance and quality control resources.
Books
The ASQ Certified Quality Auditor Handbook
The Certified Quality Inspector Handbook [CQI]
Process Quality Control: Troubleshooting and Interpretation of Data
Articles
Rethinking Statistics For Quality Control [Quality Engineer] As methods used for statistical process control become more sophisticated, it becomes apparent that the required tools have not been included in courses that teach statistics in quality control. A basic description of these tools and their applications is provided.
A Discussion Of The Software Quality Assurance Role [Software Quality Professional] The inability to identify who are actually customers limits the ability of software quality assurance engineers in the performance of their duties. Correcting this oversight enables the SQA engineer to provide greater value to customers by assuming the role of auditor as well as that of software and systems engineer.
Certifications
Quality Auditor Certification [CQA]
Quality Inspector Certification [CQI]
Courses
Certified Quality Auditor Certification Preparation
Certified Quality Auditor Question Bank
Certified Quality Inspector Certification Preparation
Certified Quality Inspector Question Bank
From The ASQ Certified Quality Auditor Handbook, ASQ Quality Press.