Results of the U. S. Geological Survey's analytical evaluation program for standard reference samples distributed in April 2001

This report presents the results of the U.S. Geological Survey's analytical evaluation program for
six standard reference samples -- T-165 (trace constituents), M-158 (major constituents), N-69
(nutrient constituents), N-70 (nutrient constituents), P-36 (low ionic-strength constituents), and
Hg-32 (mercury) -- that were distributed in April 2001 to laboratories enrolled in the U.S.
Geological Survey sponsored interlaboratory testing program. Analytical data received from 73
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.