Shewhart is most widely recognized for his control chart development and statistical contributions through Bell Laboratories.
Indeed, the Shewhart charts (e.g., X-bar and R charts) have become fundamental tools of quality control; but, of wider impact, Shewhart published, in 1931, Economic Control of Quality of Manufactured Product, a landmark book in modern quality control.
His book was used by the Japanese after World War II, with the aid of visiting consultants, to help shape modern quality practice in Japan.
Shewhart, using a literal definition of quality (Latin qualitas, from qualis, meaning "how constituted"), defined two common aspects of quality:
(1) "objective quality," which deals with the quality of a thing as an "objective reality" (of the thing) independent of the existence of man and
(2) "subjective quality," which deals with the quality of a thing relative to what man thinks, feels, or senses as a result of the "objective reality."
Shewhart linked the subjective quality property with value and concluded "it is impossible to think of a thing as having goodness independent of some human want."
This definition has been expanded by Ishikawa to include "true" (customer-language based) and "substitute" (technical-language-based) quality characteristics which form the basis for modem quality planning and quality function deployment.
It is of great historical interest to point out that the Shewhart postulates (lines of reasoning) and general conclusions published in 1931 laid the foundation for modern quality theory and practice throughout the industrial world.
His general conclusions are stated below:
It seems reasonable to believe that there is an objective state of control, making possible the prediction of quality within limits even though the causes of variability are unknown....It has been pointed out that by securing this state of control, we can secure the following advantages:
Reduction in the cost of inspection.
Reduction in the cost of rejection.
Attainment of maximum benefits from quantity production.
Attainment of uniform quality even though the inspection test is destructive.
Reduction in tolerance limits where quality measurement is indirect.
