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References and notes

1 Bernert JT, Jacob III P, Holiday DB et al. Interlaboratory comparability of serum cotinine measurements at smoker and nonsmoker concentration levels: A round robin study. Nicotine Tob Res. 2009; 11:1458-66.

2 Westgard rules are a statistical approach to evaluation of day-to-day analytical performance. The Westgard multirule quality control procedure uses five different control rules to judge the acceptability of an analytical run (rather than the single criterion or single set of control limits used by single-rule quality control systems, such as a Levey-Jennings chart with control limits set as either the mean plus or minus 2 standard deviations or the mean plus or minus 3 standard deviations). Westgard rules are generally used with two or four control measurements per run. This means they are appropriate when two different control materials are measured once or twice per material, which is the case in many chemistry applications. Some alternative control rules are more suitable when three control materials are analyzed, which is common for applications in haematology. More detail is available at

3 Westgard JO, Barry PL, Hunt MR, Groth T. A multi-rule Shewhart chart for quality control in clinical chemistry. Clin Chem. 1981; 27:493-501.

4 Westgard JO, Klee GG. Quality Management. Chapter 16 in Burtis C (ed.). Fundamentals of Clinical Chemistry. 4th edition. Philadelphia: WB Saunders Company, 1996, pp.211-23.


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