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WATERSHED MANIPULATION PROJECT: CASE STUDY OF AN INTERLABORATORY COMPARISON PROGRAM
Citation:
Erickson, H. AND D. Coffey. WATERSHED MANIPULATION PROJECT: CASE STUDY OF AN INTERLABORATORY COMPARISON PROGRAM. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-92/097.
Description:
Assessing and achieving interlaboratory comparability is a major quality assurance challenge for large interdisciplinary, multi-institutional, environmental research projects. ight laboratories routinely measure chemical constituents of various field and laboratory derived solution samples as part of the U.S. EPA's Watershed Manipulation Project. uarterly interlaboratory comparison study has been designed by EPA quality assurance personnel in Corvallis, OR (USA) to assess: 1) intralaboratory precision and accuracy, 2) interlaboratory precision, and 3) trends through time. ynthetic solution samples are prepared quarterly and sent via overnight express to participating laboratories. or each analyte, laboratories are requested to perform analyses in triplicate with each replicate measured under different calibrations; precision calculated from resulting data therefore includes a component of among-batch variability. elative bias is calculated as the percent difference between a laboratory's mean and the median of the laboratories (the supplying laboratory's value being treated equally to the other laboratories). verall precision is expressed as the coefficient of variation using laboratory means. n ANOVA approach is also used to calculate significant differences among laboratories. ata interpretation and results from four quarterly evaluations will be presented.