8Belk W P, Sunderman, F W. A survey of the accuracy of chemical analyses in clinical laboratories[-J]. American Journal of Clinical Pathology, 1947,17(11): 853-861.
9Sunderman F W. The history of proficiency testing/ quality control [J]. Clinical Chemistry, 1992, 38 (7) : 1205-1209.
10Laessig R H, Ehrmeyer S S. Proficiency testing pro- grams-promises, progress, and problems. A 40-year prospective[J]. Archives of pathology & laboratory medicine, 1988,112 (4) : 329-333.