Quality

Quality refers to the distinctive characteristics or properties of a person, object, process or other thing. Such characteristics may enhance a subject's distinctiveness, or may denote some degree of achievement or excellence. When used in relation to people, the term may also signify a personal character or trait. When used in relation to management, the term may be easily defined as "reduction of variability" or "compliance with specifications".

The term is sometimes contrasted with the concept of quantity. In science, the work of Aristotle focused on measuring quality, whereas the work of Galileo resulted in a shift towards the study of quantity.

Quality can be used as a tool of measurement, like metric or fahrenheit, as it is used to judge both subjects that are esteemed as credible and agreeable as "high quality" and subjects that are viewed as confusing, offensive, unhelpful, or incredible as "low quality." But quality is also used as a positive word, as in the sense of "this is a quality chair." Its antonym can be perceived as poorness, incredibility, unhelpfulness, and a variety of other words that reflect the concept of having low quality.

ISO 9000 defines quality as "degree to which a set of inherent characteristic fulfils requirements".

In manufacturing
"Quality" as defined by the American Society for Quality is "the characteristics of a product or service that bear on its ability to satisfy stated or implied needs." Therefore, the quality of a product relates to how well the product serves the needs of the customer; as perceived by the customer.

Many different techniques and concepts have evolved to improve manufacturing quality, including SPC, Zero Defects, Six Sigma, quality circles, TQM and continuous improvement.

Historical development of the concept
The meaning for the term quality has developed over time. Seven distinctive interpretations:


 * 1) "Conformance to specifications" (Phil Crosby in the 1980s). The difficulty with this is that the specifications may not be what the customer wants; Crosby treats this as a separate problem.
 * 2) "Fitness for use" (Joseph M. Juran). Fitness is defined by the customer.
 * 3) A two-dimensional model of quality (Noriaki Kano and others). The quality has two dimensions: "must-be quality" and "attractive quality". The former is near to the "fitness for use" and the latter is what the customer would love, but has not yet thought about. Supporters characterise this model more succinctly as: "Products and services that meet or exceed customers' expectations". One writer believes (without citation) that this is today the most used interpretation for the term quality.
 * 4) "Value to some person" (Gerald M. Weinberg)
 * 5) (W. Edwards Deming), "Quality is pride of workmanship."  See http://www.deming.org/
 * 6) "The loss a product imposes on society after it is shipped"(G. Taguchi), Taguchi’s definition of quality is based on a more comprehensive view of the production system.
 * 7) Energy quality, associated with both the energy engineering of industrial systems and the qualitative differences in the trophic levels of an ecosystem.

In music
In music quality refers primarily to the timbre, but also dynamics and musical texture, of a section or piece.

In phonetics
In phonetics quality refers to the articulatory features that distinguish vowels and to their acoustic correspondent. Vowel quality is opposed to vowel quantity.

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