Quality Control & Quality Assurance – What Is the Difference?

Juran Knowledge

It is often assumed that quality control and quality assurance are one and the same thing—however, while both are an essential component of quality management systems there are some subtle but important differences between the two activities.

What is quality control?

Quality control (QC) is concerned with the identification of defects—as such, it is regarded as the “inspection” element of quality management. It is the third universal process in the Juran Trilogy, alongside quality planning and quality improvement.

Compliance with quality standards—such as those enshrined in ISO 9001—is a key part of quality control. According to these standards, quality control is focused on three aspects:

  1. Job management, controls, clearly defined and well managed processes, performance criteria, and identification of records

  2. Competence—such as skills, experience, qualifications and knowledge

  3. Softer elements including personnel, confidence, motivation, quality relationships, and organizational culture.

If any of these three aspects are deficient in any way, the quality of output is likely to suffer, whether that’s a product or a service. Common approaches to quality control include statistical process control and root cause corrective action.

What is quality assurance?

Whereas quality control focuses on identifying defects, quality assurance (QA) focuses on the prevention of defects. It is defined by ISO 9000 as the “part of quality management focused on providing confidence that quality requirements will be fulfilled”.

The emphasis of quality assurance is less on the end product, and more on the processes and systems involved in creating it. For this reason, auditing is an important part of the quality assurance function–particularly quality auditing, which examines an organization’s entire quality management system (QMS).

Quality assurance has two key principles:

  1. Fit for purpose – the product should be suitable for its intended purpose

  2. Right first time – all defects or mistakes should be eliminated.

Quality assurance approaches

Quality assurance encompasses a number of activities and approaches—all sharing quality improvement as a common objective.

Failure testing

Failure or stress tests are a common way of uncovering potential product weaknesses ahead of time. In such tests, a product will be operated until it fails, typically under “stressful” conditions such as increased temperature, speed, or humidity. The data from these tests is then used to deliver improvements to the manufacturing or engineering process.

Total quality management (TQM)

Originating in the 1950s, the concept of total quality management (TQM) refers to company-wide efforts to improve the quality of processes and products, thus delivering greater value to the customer.

At Juran, we use the term ‘enterprise excellence’ as an alternative to TQM. Our Enterprise Excellence Management System is geared towards developing a culture or delivering products and services that will exceed customer, regulatory, business, and societal needs.

Standards and models

There are various models and standards that provide a regulatory framework for quality assurance. For example, ISO 7025 specifies what testing and calibration laboratories must do to become accredited, specifying a number of management and technical requirements.

Elsewhere, the Capability Maturity Model Integration (CMMI) model is used as a quality improvement tool by many organizations, and is required for many government contracts, especially in software development.