References
- Groff , J. H. , Schlecht , P. C. and Shulman , S. 1990 . Laboratory Reports and Rating Criteria for the Proficiency Analytical Testing (PAT) Program Cincinnati, OH : U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health . DHHS (NIOSH) Pub. No. 91-102.