Statistical Procedures for Determination and Verification of Minimum Reporting Levels for Drinking Water Methods

• Published in: Environmental science & technology 2006-01, Vol.40 (1), p.281-288
• Main Authors: Winslow, Stephen D, Pepich, Barry V, Martin, John J, Hallberg, George R, Munch, David J, Frebis, Christopher P, Hedrick, Elizabeth J, Krop, Richard A
• Format: Article
• Language: English
• Subjects: Analysis of Variance; Applied sciences; Calibration; Data Interpretation, Statistical; Drinking water; Drinking water and swimming-pool water. Desalination; Environmental Exposure - statistics & numerical data; Environmental science; Exact sciences and technology; Laboratories; Pollution; Regression analysis; Statistical analysis; Tests; United States; United States Environmental Protection Agency; Water Pollutants - analysis; Water Pollutants - toxicity; Water Supply - analysis; Water Supply - standards; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es051069f

The United States Environmental Protection Agency's Office of Ground Water and Drinking Water has developed a single-laboratory quantitation procedure:  the lowest concentration minimum reporting level (LCMRL). The LCMRL is the lowest true concentration for which future recovery is predicted to fall, with high confidence (99%), between 50% and 150%. The procedure takes into account precision and accuracy. Multiple concentration replicates are processed through the entire analytical method and the data are plotted as measured sample concentration (y-axis) versus true concentration (x-axis). If the data support an assumption of constant variance over the concentration range, an ordinary least-squares regression line is drawn; otherwise, a variance-weighted least-squares regression is used. Prediction interval lines of 99% confidence are drawn about the regression. At the points where the prediction interval lines intersect with data quality objective lines of 50% and 150% recovery, lines are dropped to the x-axis. The higher of the two values is the LCMRL. The LCMRL procedure is flexible because the data quality objectives (50−150%) and the prediction interval confidence (99%) can be varied to suit program needs. The LCMRL determination is performed during method development only. A simpler procedure for verification of data quality objectives at a given minimum reporting level (MRL) is also presented. The verification procedure requires a single set of seven samples taken through the entire method procedure. If the calculated prediction interval is contained within data quality recovery limits (50−150%), the laboratory performance at the MRL is verified.