Statistical analysis of measured actinide concentration bias in a Mixed Analyte Performance Evaluation Program

Data from seven Mixed Analyte Performance Evaluation Program studies have been used to identify specific problems with results and/or laboratories. These data have never been used to determine the bias or variability in data reporting for these laboratories in general. These historical analytical data were analyzed for accuracy and precision overall and separated by method of sample preparation, method of sample pretreatment, method of detection and sample size. The calculated mean percent relative bias was analyzed for the actinides (²⁴¹Am, ²³⁸Pu, ^239/240Pu, ^234/233U, and ²³⁸U) in the soil and water standards. Results from most analysis methods were at least slightly negatively biased. For the water standards, the overall 95% confidence interval for the mean percent relative bias was −1.6% to −0.5% indicating that the average actinide results slightly underestimated the true concentration. For the soil standards, the overall 95% confidence interval for the mean percent relative bias was −8.1% to −6.6% indicating that the average actinide results moderately underestimated the true concentration. This revised version was published online in July 2006 with corrections to the Cover Date.