Reliability is the probability that the product or service will perform it intended function for a specified length of time. Durability is defined as the length of time a product functions. Quality of conformance is a measure of how a product meet its specifications. For example, the specifications for a machined part may be a drilled hold that is three inches in diameter, plus or minus 1/8 inch. Part falling within this range are defined as conforming parts. Fitness for use is the suitability of the product for carrying out its advertised functions. If there is a fundamental design flaw, the product may fail in the field even if it conforms to its specifications. Product recall are frequently the result of fitness-for-use failures.
Improving quality, than, means improving one or more of the eight quality dimensions while maintaining performance on the remaining dimensions. Providing a higher-quality product than a competitor means outperforming the competitor on at least one dimension while matching performance on the remaining dimensions. Although all eight dimensions are important and can affect customer satisfaction, the quality attributes that are measurable tend to receive more emphasis. Conformance, in particular, is strongly emphasized. In fact, many quality experts believe that “quality is conformance” is the best operational definition. There is some logic to this position. Product specifications should explicitly consider such things as reliability, durability, fitness for use and performs well. The product should be produced as the design specifies it; specifications should be met. Conformance is the basis for defining what meant by a nonconforming, or defective, product.