Results of the U.S. Geological Survey's analytical evaluation program for standard reference samples distributed in October 1999

This report presents the results of the U.S. Geological Survey's analytical evaluation program for six standard
reference samples -- T-159 (trace constituents), M-152 (major constituents), N-63 (nutrient constituents), N-64
(nutrient constituents), P-33 (low ionic strength constituents), and Hg-29 (mercury) -- that were distributed in
October 1999 to 149 laboratories enrolled in the U.S. Geological Survey sponsored interlaboratory testing program.
Analytical data that were received from 131 of the laboratories were evaluated with respect to overall laboratory
performance and relative laboratory performance for each analyte in the six reference samples. Results of these
evaluations are presented in tabular form. Also presented are tables and graphs summarizing the analytical data
provided by each laboratory for each analyte in the six standard reference samples. The most probable value for
each analyte was determined using nonparametric statistics.