Continuous Improvement in Continuous Quality Control

“Quality is never an accident. It is always the result of intelligent effort.” So observed John Ruskin, Victorian writer and critic of art, architecture, and society (1), unknowingly foreshadowing the emergence of quality science in the 20th century. Statistical QC came from Bell Telephone Laboratories, where Shewhart developed the statistical control chart in 1924, and Dodge and Romig pioneered statistical methods for acceptance sampling rather than 100% inspection of products. These beneficial techniques were not widespread until the manufacturing demands of World War II necessitated better control of product quality. With Deming's involvement, quality science was further developed in postwar Japanese manufacturing (2). Levey and Jennings introduced clinical laboratory statistical QC in 1950 (3). The Levey–Jennings chart remains a staple of laboratory QC. Development of stabilized control materials enhanced QC practices (4), and the testing of controls at fixed intervals became and remains the QC mainstay. Control-based QC has many strengths, including sensitivity to small changes in bias and ready availability of controls. Test intervals may be adjusted to account for assay stability, regulations or a laboratory's experience. Decision rules may be selected to maximize both sensitivity and specificity of QC procedures (5, 6).