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• Section No 14 <br /> Revision No 0 <br /> Date September 5, 1991 <br /> Page 2 of 4 <br /> 14 2 Precision <br /> Precision is defined as the relative percent difference of matrix spike <br /> recoveries for two matrix spikes of the same sample (replicates) and is <br /> evaluated in terms of the relative percent difference Because of the <br /> limited number of replicate samples that can be analyzed in environmental <br /> samples using gas chromatograph techniques, precision cannot be evaluated in <br /> terms of standard deviations. Consequently, outlier testing is not possible <br /> However, the precision of an analytical method can be evaluated from <br /> internal lab and field duplicates by calculating the percent differences <br /> between the duplicate sample results <br /> • PD — 2 D1-D2 x 100 <br /> (Dl+D2) <br /> where <br /> PD = Percent Difference <br /> Dl — First Sample Value <br /> D2 = Second Sample Value (duplicated) <br /> 14 3 Completeness <br /> Completeness is described as the ratio of acceptable laboratory results <br /> to the total number of analyses performed A completeness value of less than <br /> 95% indicates that corrective action is necessary in order to limit the <br /> number of defective results <br /> Criteria for defective results may include exceeded holding times, <br /> • percent recoveries outside the limits, or unsatisfactory supporting data such <br /> 14-2 <br />