My Definition of Quality
Quality is a contextual concept with both subjective and objective aspects, not directly measurable as a whole, consisting of three interconnected but independently varying parts:
External quality is the relationship between the value a product or service delivers and the person who matters, evaluated by how that value aligns with or diverges from their needs, requirements, and expectations simultaneously.
Delivery quality is the experience the person who matters feels before, during, and after the process of delivering a product or a service, shaped by multiple dimensions.
Internal quality is a predictable discipline, tracked and continuously improved through its measurable characteristics and indicators, a pursuit of excellence with which an organization and its people produce a product or service for the person who matters.
Research Base
Note: This Sankey diagram is dynamic. If you click on the nodes it will filter the table below it.
| When | Who | Term Defined | Description |
|---|---|---|---|
| ~350 BC | Aristotle | Quality | Quality as a category of being: that in virtue of which things are said to be qualified somehow. Distinguished between essential properties and accidental properties. |
| ~100 BC | Cicero | Qualitas | Cicero coined the Latin word "qualitas" as a translation of the Greek "poiotēs" (ποιότης), meaning "of what kind." |
| 1931 | Walter A. Shewhart | Quality | Quality has two aspects: (1) objective quality — the physical characteristics of a thing, independent of the existence of man; (2) subjective quality — what we think, feel, or sense as a result of the objective reality. |
| 1950s–1986 | W. Edwards Deming | Quality | A predictable degree of uniformity and dependability at low cost and suited to the market. Quality should be aimed at the needs of the customer, present and future. |
| 1951/1961 | Armand V. Feigenbaum | Quality (Total Quality Control) | The total composite of product and service characteristics of marketing, engineering, manufacture, and maintenance through which the product and service in use will meet the expectations of the customer. |
| 1951/1954 | Joseph M. Juran | Quality | "Fitness for use." Meaning a product or service meets the customer's needs and is free from deficiencies (defects, errors, or failures). |
| 1960s | Kaoru Ishikawa | Quality (Company-Wide) | Quality encompasses the entire organization — not just the product, but after-sales service, management, the company itself, and the people within it. The customer defines quality, not the producer. Within an organization, the next process is your customer. |
| 1974 | Robert M. Pirsig | Quality | Quality is neither mind nor matter, but a third entity independent of the two... even though Quality cannot be defined, you know what it is. Quality is the continuing stimulus which our environment puts upon us to create the world in which we live. |
| 1977 | Jim McCall et al. | Software Quality | Software quality is characterized through 11 quality factors organized into three perspectives: Product Operations (correctness, reliability, efficiency, integrity, usability), Product Revision (maintainability, flexibility, testability), and Product Transition (portability, reusability, interoperability). |
| 1978 | Barry W. Boehm et al. | Software Quality | Software quality is defined through a hierarchical model of characteristics: primary uses (as-is utility, maintainability, portability) decomposed into intermediate constructs (reliability, efficiency, usability, testability, understandability, flexibility) and primitive constructs. |
| 1979 | Philip B. Crosby | Quality | Conformance to requirements. |
| 1982/1984 | Christian Grönroos | Perceived Service Quality | The outcome of an evaluation process where the customers compare their expectations with the service they have received. Quality has two dimensions: technical quality (what the customer receives) and functional quality (how the service is delivered). |
| 1984 | David A. Garvin | Quality (5 Approaches) | Five approaches: (1) Transcendent — innate excellence, recognized but not definable; (2) Product-based — measurable differences in attributes; (3) User-based — fitness for intended use / satisfying preferences; (4) Manufacturing-based — conformance to requirements/specifications; (5) Value-based — quality relative to price/cost. |
| 1984 | Noriaki Kano et al. | Attractive Quality & Must-Be Quality | Quality is not one-dimensional. Product/service attributes have nonlinear, asymmetric impacts on customer satisfaction, categorized as: Must-be quality (basic expectations), One-dimensional quality (proportional satisfaction), Attractive quality (unexpected delight), Indifferent quality, and Reverse quality. |
| 1985/1988 | Parasuraman, Zeithaml & Berry | Service Quality (Gap Model) | Service quality is the gap or difference between customer expectations and perceptions of actual service performance. Measured across five dimensions: Reliability, Assurance, Tangibles, Empathy, and Responsiveness (RATER). |
| 1986 | ISO 8402:1986 | Quality | The totality of features and characteristics of a product or service that bear on its ability to satisfy stated or implied needs. |
| 1986 | Genichi Taguchi | Quality | Quality is the loss a product causes to society after being shipped, other than any losses caused by its intrinsic functions. |
| 1986/1987 | Six Sigma (Motorola / Bill Smith) | Six Sigma Quality | Six Sigma strategies seek to improve manufacturing quality by identifying and removing the causes of defects and minimizing variability in manufacturing and business processes. A quality standard of no more than 3.4 defects per million opportunities (DPMO), corresponding to 99.99966% defect-free output. Quality is defined as reducing process variation so that six standard deviations fit between the process mean and the nearest specification limit. |
| 1987/1992 | Robert Grady / Hewlett-Packard | Software Quality (FURPS) | Quality is classified through five attributes: Functionality (capability, reusability, security), Usability (human factors, aesthetics, documentation), Reliability (availability, predictability, accuracy), Performance (speed, efficiency, throughput, scalability), and Supportability (testability, flexibility, installability). |
| 1987/1988 | Malcolm Baldrige National Quality Award (U.S. Congress) | Performance Excellence | Quality as performance excellence: the delivery of ever-improving value to customers and stakeholders, contributing to organizational sustainability, organizational learning, and management by facts. Assessed across seven criteria: Leadership, Strategy, Customers, Measurement/Analysis/Knowledge Management, Workforce, Operations, and Results. |
| 1987/1991 | CMM/CMMI (Watts Humphrey / SEI) | Process Quality / Maturity | Quality is achieved through process maturity — the degree to which an organization's processes are defined, managed, measured, and continuously optimized. Five maturity levels: Initial, Managed, Defined, Quantitatively Managed, and Optimizing. |
| 1989 | Watts Humphrey | Software Quality | Quality is the result of disciplined, well-defined processes. Software quality cannot be achieved through testing alone — it must be built in through process maturity, personal discipline, and continuous measurement. The quality of software is governed by the quality of the process used to develop it. |
| 1990 | IEEE Std 610.12-1990 | Software Quality | (1) The degree to which a system, component, or process meets specified requirements. (2) The degree to which a system, component, or process meets customer or user needs or expectations. |
| ~1990s | IBM | Quality | Market-driven quality |
| 1991 | ISO/IEC 9126:1991 | Software Product Quality | Software quality is characterized by six characteristics: Functionality, Reliability, Usability, Efficiency, Maintainability, and Portability. |
| 1991/1992 | EFQM (European Foundation for Quality Management) | Organizational Excellence | Organizational excellence is the ability to achieve and maintain exceptional results simultaneously for all stakeholders. Excellence is measured through a non-prescriptive framework of Enablers (what an organization does) and Results (what it achieves), connected through continuous learning and innovation. |
| 1992 | Gerald Weinberg | Quality | Quality is value to some person. |
| 1995/1997 | Edward Yourdon / James Bach | "Good Enough" Software Quality | Quality is not absolute but contextual — the optimal level of quality may not be perfect, and how much less than perfect depends on the specific business context. Quality must be balanced against cost, schedule, staffing, and functionality constraints. |
| 1995 | R. Geoff Dromey | Software Product Quality | Software quality is determined by the tangible quality-carrying properties of software components (correctness, internal, contextual, descriptive), linked to high-level quality attributes. Quality evaluation differs for each product, requiring a dynamic model connecting measurable product properties to attributes like reliability, maintainability, efficiency, usability, reusability, and portability. |
| 1996 | Kitchenham & Pfleeger | Software Quality (Five Perspectives) | Software quality is an elusive, multi-perspective concept. Following Garvin, five views are identified: (1) Transcendental — "we know it when we see it"; (2) User — appropriateness for context of use; (3) Manufacturing — conformance to requirements (most popular view, held by ~50% of practitioners); (4) Product — internal, inherent characteristics; (5) Value — quality relative to price. |
| 2000 | ISO 9000:2000 | Quality | Degree to which a set of inherent characteristics fulfils requirements. |
| ~2000s | Tom DeMarco | Quality | A product's quality is a function of how much it changes the world for the better. |
| ~1999/2001 | Cem Kaner / James Bach / Michael Bolton (Context-Driven School) | Quality (in testing context) | Quality is value to some person who matters. Product quality is a relationship between a product and people, never an attribute that can be isolated from a human context. |
| 2001 | Agile Alliance (Beck, Fowler, Cockburn, Sutherland et al.) | Software Quality (implicit) | Working software is the primary measure of progress. Our highest priority is to satisfy the customer through early and continuous delivery of valuable software. Continuous attention to technical excellence and good design enhances agility. |
| 2001 | ISO/IEC 9126-1:2001 | Software Product Quality | Software product quality is modeled in two parts: (a) internal quality and external quality — six characteristics: Functionality, Reliability, Usability, Efficiency, Maintainability, Portability; (b) quality in use — four characteristics. |
| ~2004 | PMBOK (PMI) | Quality (Project Management) | The degree to which a set of inherent characteristics fulfills requirements. Quality management is the activity of developing quality products and services required to meet customer expectations using quality processes and procedures. |
| 2005/2010 | Roger S. Pressman | Software Quality | An effective software process applied in a manner that creates a useful product that provides measurable value for those who produce it and those who use it. |
| 2011 | ISO/IEC 25010:2011 | Software Product Quality / Quality in Use | Product quality model: eight characteristics — Functional Suitability, Performance Efficiency, Compatibility, Usability, Reliability, Security, Maintainability, Portability. Quality in use model: five characteristics — Effectiveness, Efficiency, Satisfaction, Freedom from Risk, Context Coverage. |
| 2014 | SWEBOK v3.0 (IEEE Computer Society) | Software Quality | Software quality may refer to: desirable characteristics of software products, the extent to which a particular software product possesses those characteristics, and processes, tools, and techniques used to achieve those characteristics. Defined as "the capability of software product to satisfy stated and implied needs under specified conditions" and "the degree to which a software product meets established requirements." |
| 2015 | ISO 9000:2015 | Quality | Degree to which a set of inherent characteristics of an object fulfils requirements. |
| 2023 (v3.7) | ISTQB Glossary v3.7 | Quality | The degree to which a component, system or process meets specified requirements and/or user/customer needs and expectations. |
| 2023 | ISO/IEC 25010:2023 | Software Product Quality | Product quality model: nine characteristics — Functional Suitability, Performance Efficiency, Compatibility, Interaction Capability, Reliability, Security, Maintainability, Portability, Safety. Replaces "Usability" with broader "Interaction Capability" and adds "Safety". |
| Current | Oxford English Dictionary | Quality | The standard of something as measured against other things of a similar kind; the degree of excellence of something. |
| Current | Collins English Dictionary | Quality | (1) A distinguishing characteristic, property, or attribute. (2) The basic character or nature of something. (3) A trait or feature of personality. (4) Degree or standard of excellence. |
| Current | ASQ (American Society for Quality) | Quality | A subjective term for which each person or sector has its own definition. In technical usage, quality can have two meanings: (1) the characteristics of a product or service that bear on its ability to satisfy stated or implied needs; (2) a product or service free of deficiencies. |