The meaning of quality

Quality is often referred to as the “degree or grade of excellence”; thus, it is a relative measure of goodness. Defining quality as goodness is so general that it offers no operational content. Adopting a customer focus provides operational content. Operationally, a quality product or service is one that meets or exceeds customer expectations. Customerexpectations relate to attributes such as product performance, reliability, durability, and fitness for use. A quality specification is the specific level of performance  planned for a given quality attribute. Customers expect a quality product or service to perform according to specifications. Quality of conformance is a measure of how a product meets its specifications.

Conformance is strongly emphasized because it is the key to meeting customer expectations. In fact, most quality experts believe that “quality is conformance” is the best operational definition of quality. There is some logic to this position. Product specifications should explicitly consider such things as reliability, durability, fitness for use, and performance. Implicitly, a conforming product is reliable, durable, fit for use, and performs well. The product should be produced as specified by the design; specifications should be met. Conformance is the basis for defining what is meant by a nonconforming,or defective, product.

 Read defining quality costs.

defective product is one that does not conform to specifications. Zero defects means that all products conform to specifications. But what is meant by “conforming to specifications”? Traditional conformance defines an acceptable range of values for each specification or quality characteristic. A target value is defined, and upper and lower limits are set that describe acceptable product variation for a given quality characteristic. Any unit that falls within the limits is deemed nondefective. For example, the targeted specification for a machined part may be a drilled hole that is two inches in diameter, and any part that is within 1/32 inch of the target is acceptable. On the otherhand, the robust quality view of conformance emphasizes exactness of conformance. Robustness means exact conformance to the target value (no tolerance allowed). There is no range in which variation is acceptable. A nondefective machine part in the robust setting would be one that has a drilled hole that measures exactly two inches. Since evidence exists that product variation can be costly, the robust quality definition of conformance = is superior to the traditional definition.

An example of the difference between the traditional approach and the robust quality approach can be found in two plants of the Sony Corporation. Both the Tokyo and the San Diego plants produce color television sets. One important feature of a color television set is color density. Sony sets a target value for color density as well as an upper specification limit and a lower specification limit. Any set with color density falling outside the specification limits is considered defective. Does that mean any set falling within the specification limits is acceptable? The viewpoint differs between the two plants. The San Diego plant emphasized zero defects in the traditional sense. In evaluating the quality of the color density of television sets, any television falling within the specification limits was deemed acceptable and shipped to customers. Sony of Tokyo, working with a robust quality viewpoint, strove to hit the target value for color density. Exhibit 14-1, on the following page, illustrates the distribution of color density of television sets shipped from the two plants.

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