Historical Data Structure and Laboratory Performance in the North American Proficiency Testing (NAPT) Program.
Grant E. Cardon, Utah State University, Logan, UT, Bryan G. Hopkins, Plant & Wildlife Sciences, Brigham Young University, Provo, UT, John R. Lawley, Plants, Soils, and Climate, Utah State University, Logan, UT and Tony L. Provin, Soil and Crop Sciences, Texas A&M AgriLife Extension, College Station, TX, US