The BSP quality-control data published on the CD-ROM include 34 dissolved chemical constituents for the water years 1985 to 1995. These data apply to the laboratory methods used to analyze WQN stream water-quality samples for dissolved chemical constituents during this period.
The purpose of the BSP is to monitor, assure, and improve the quality of laboratory analytical results through the use of blind quality-control samples. The BSP regularly submits to participating USGS laboratories reference water samples having known chemical concentrations and consisting of a stable, homogeneous chemical and physical matrix. The reference samples are subject to the identical laboratory handling, processing, and analytical procedures as those applied to environmental samples.
BSP samples have been used by the USGS as an independent source to verify the accuracy (bias and variability) of laboratory analytical methods and ambient water-quality measurements. Estimates of the bias and variability of laboratory analytical measurements provide quantitative information about the extent to which lab methods contribute to systematic and random variations in measurements of ambient stream water quality, respectively.
See the accompanying Open-File Report for a discussion of the characteristics of the BSP data and statistical methods for using these data to estimate laboratory measurement bias and variability and to assist in the interpretation of national network stream water-quality data.
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Estimates of laboratory measurement error and variability are organized in separate files by constituent group. Measurement error data from which the bias can be estimated appear in the file BIAS.ttt, and laboratory measurement variability data appear in the file VAR.ttt, where ttt is:
Measurement variability data are available in the following files (see the VAR.FMT file for details of the file layout):