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Evaluation of Match Criteria Used for the Comparison of Refractive Index of Glass Fragments§

Authors

  • Elizabeth J. Garvin B.S.,

    1. Visiting Scientist and Research Chemist, Counterterrorism and Forensic Science Research Unit, FBI Laboratory, FBI Academy, Quantico, VA 22135.
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  • Robert D. Koons Ph.D.

    1. Visiting Scientist and Research Chemist, Counterterrorism and Forensic Science Research Unit, FBI Laboratory, FBI Academy, Quantico, VA 22135.
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    • The publication does represent work done by the FBI.


  • Presented at the 61st Annual Meeting of the American Academy of Forensic Sciences, February 20, 2009, in Denver, CO.

  • The Visiting Scientist Program is an educational opportunity funded by the FBI Laboratory and administered by the Oak Ridge Institute for Science and Education.

  • §

    Publication No. 09-07 of the Laboratory Division of the Federal Bureau of Investigation (FBI). Mention of trade names is for information purposes only and does not imply endorsement by the FBI or the federal government.

  • Retired. Present address: 2070 Farragut Drive, Stafford, VA 22554.

Additional information—reprints not available from author:
Robert D. Koons, Ph.D.
2070 Farragut Drive
Stafford, VA 22554
E-mail: rdkoons@verizon.net

Abstract

Abstract:  For comparative glass examinations, the refractive indices (RIs) of recovered glass fragments are often compared to a test interval defined by measurements from a broken glass object. RI measurements from five modern float glasses were used via resampling to assess the frequencies of false exclusion errors for eight test criteria as functions of the number of measurements. The test criteria were based on ranges, fixed intervals, and multiples of standard deviations of the known source measurements. The observed error rates for the eight tests studied are between zero and c. 35%, depending upon the match criteria, the number of measurements, and the RI distribution for a glass source. The results of this study can be used to predict the false exclusion rate for a test criterion under a given set of conditions or to select test criteria that result in a desired error rate for these typical sheet glasses.

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