Methodological approaches to calculation of the main validation parameters of forensic techniques

Validation of the forensic methods (FM) is one of the main procedures for the standardization of forensic activities used to verify the reliability of the obtained results of the studies. This procedure is widely adopted in the organizations of the European Network of Forensic Science Institutes (ENFSI), which also includes the Russian Federal Centre of Forensic Science of the Ministry of Justice of the Russian Federation (RFCFS). Two types of FM can be distinguished in metrological aspects: forensic method of measurements (FMM) and forensic methods of testing (FMT). We have shown earlier that unlike the developed methodological approaches to the FMM validation which gained practical application in the RFCFS laboratories, the FMT validation procedures give rise to many questions which are widely discussed in the scientific literature. The most significant difficulties in FM validation are attributed to selection of the validation parameters, development of the validation experiment and performance of statistical calculations. We propose methodological approaches to the statistical assessment of the FMM and FMT parameters to be used in practice of forensic experts. Moreover, we present a number of recommendations on the validation procedure, list of the validation parameters, and consider specific schemes of the experiments to be used for assessing of the quality indicators of FMM and FMT. The results of multiple determination of the controlled index in the referenced samples and standard additives are presented to assess the suitability of the FMM using common formulas for calculation of the statistical parameters. Case study of the FMT validation procedure «Microscopic Examination of Textile Fibers» is considered. The expediency of using probabilistic estimate of the share of false test results, as well as calculation of the likelihood ratio in assessing the reliability of forensic methods of testing and competence of the experts is demonstrated.

1. Smirnova S. A., Omelianyuk G. G., Bebeshko G. I. Methodological approaches to the validation of forensic methods, including measurement methods (MI) / Teor. Prakt. Sud. Ékspert. 2012. N 1(25). P. 50 – 62 [in Russian].

2. State Standard GOST R ISO 5725–2002. Accuracy (truness and precision) of measurement methods and results. Part 1 – 6. — Moscow: Izd. standartov, 2002 [in Russian].

3. RMG-61–2010. Accuracy, trueness and precision measures of the procedures for quantitative chemical analysis. Methods of evaluation. — Moscow: Standartinform, 2013. — 59 p. [in Russian].

4. EURACHEM/CITAC Guide CG 4. Quantifying uncertainty in analytical measurement, Third edition. QUAM:2012.P1.

5. Smirnova S. A., Omelianyuk G. G., Usov A. I., Bebeshko G. I. Special considerations in applining the key terms and definitions of the international standard GOST ISO/IEC 17025–2009 in forensic science laboratories / Teor. Prakt. Sud. Ékspert. 2012. N 2(26). P. 57 – 67 [in Russian].

6. Paneva V. I. Assessment of the suitability of quantitative analysis methods in the laboratory / Zavod. Lab. Diagn. Mater. 2008. Vol. 74. N 8. P. 68 – 72 [in Russian].

7. Prichard E., Barwik V. Quality assurance in analytical chemistry. — Wiley, 2007. — 316 p.

8. International vocabulary of metrology. — St. Peterburg: Professional, 2010. — 82 p. [in Russian].

9. ISO Guide 99–2007. International vocabulary of metrology. Basic and general concepts and associated terms (VIM). http://www.iso.org/standard/45324.html.

10. Bebeshko G. I., Omelianyuk G. G., Nikulina M. V., Valitova A. R. A practice of validation of method of determination of pH and specific electrical conductivity in the objects of soil-geological origin for production of forensic environmental examination in the absence of standard samples / Teor. Prakt. Sud. Ékspert. 2017. Vol. 12. N 2. P. 66 – 74 [in Russian].

11. Smirnova S. A., Omelianyuk G. G., BebeshkoG. I., Yudin N. V. The experience of validation of measurement method «The determination of benzo(a)pyrene concentration in the objects of soil-geological origin by means of HPLC fluorimetry detecting method» for production of forensic environmental examination / Teor. Prakt. Sud. Ékspert. 2012. N 3(27). P. 79 – 91 [in Russian].

12. Metodical Regulations MUK 4.1.1274–03. Test methods. Chemical factors. Measurement of the mass fraction of benz(a)pyrene in soil, sediment and solid waste samples by HPLC using a fluorometric detector. — Moscow: Minzdrav Rossii [in Russian].

13. Doerffel K. Analytical science — a discipline between chemistry and metrology / Fresenius J. Anal. Chem. 1998. Vol. 363. N 5. P. 393 – 394.

14. Doerffel K. Statistics in analytical chemistry / Translated from German by V. V. Nalimov (ed.). — Moscow: Mir, 1994. — 247 p. [Russian translation].

15. Gauthier T. D. Statistical methods / Introduction to environmental forensics. Ed. by B. L. Murphy and R. D. Morrison — London: Elsivier, 2004. Ch. 10. P. 391 – 428.

16. EUACHEM/CITAC Guide. The Expression of Uncertainty in Qualitative Testing/ Committee Draft. September 2003. LGCN/ VAM/2003/048/.

17. Pulido A., Ruisaìnchez I., Boqueì R., Rius F. X. Uncertainty of results in routine qualitative analysis / Trends Anal. Chem. 2003. Vol. 22. N 10. P. 647 – 654. DOI: 10.1016/S0165-9936(03)01104-X.

18. Ellison S. L. R., Fearn T. Characterizing the performance of qualitative analytical methods: Statistics and terminology / Trends Anal. Chem. 2005. Vol. 24. N 6. P. 468 – 476. DOI: 10.1016/j.trac.2005.03.007.

19. Trullols E., Ruisaìnchez I., Rius F. X., Huguet J. Validation of qualitative methods of analysis that use control samples / Trends Anal. Chem. 2004. Vol. 23. N 2. P. 137 – 145. DOI: 10.1016/j.trac.2005.04.001.

20. Panteleimonov A. V., Nikitina N. A., Reshetnyak E. A., et al. Binary response procedures of qualitative analysis: methodological characteristics and calculation aspects / Met. Ob’’ekty Khim. Analiza. 2008. Vol. 3. N 2. P. 128 – 146 [in Russian].

21. Mil’man B. L. Introduction to forensic identification. — St. Peterburg: VVM, 2008. — 179 p. [in Russian].

22. Mil’man B. L., Konopel’ko L. A. Uncertainty of qualitative chemical analysis: General methodology and binary test methods / J. Anal. Chem. 2004. Vol. 59. N. 12. P. 1128 – 1141. DOI: 10.1023/B:SANC.0000049712.88066.e7.

23. Mil’man B. L. Identification of chemical compounds / Trends Anal. Chem. 2005. Vol. 24. N 6. P. 493 – 508. DOI: 10.1016/j.trac.2005.03.013.

24. Smirnova S. A., Bebeshko G. I., Lyubetskaya I. P., et al. Probability-Based Validation of the Forensic Method «Microscopic Analysis of Textile Fibers» / Teor. Prakt. Sud. Ékspert. 2019. Vol. 14. N 2. P. 92 – 99. DOI: 10.30764/1819-2785-2019-14-2-92-99 [in Russian].