About the Authors William D. Kelley has been an advisor for several American Society for Testing and Material Committees in the areas of statistics and laboratory quality control. Through his involvement with NIOSH and AIHA, he has developed accreditation procedures and several training courses for industrial hygiene laboratories. Thomas A. Ratliff, Jr. is a consultant in the field of industrial quality control for the EPA, NIOSH, and the Mine Safety and Health Administration. He is also a senior member of the American Society for Quality Control, a certified quality engineer and auditor, and