References
- Esche , C. A. , Groff , J. H. , Schlecht , P. C. and Shulman , S. A. 1994 . Laboratory Evaluations and Performance Reports for the Proficiency Analytical Testing (PAT) and Environmental Lead Proficiency Analytical Testing (ELPAT) Programs , Cincinnati, OH : National Institute for Occupational Safety and Health . DHHS (NIOSH) No. 95–104