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Strengthening Forensic Science in the United States: A Path Forward
terms. Although some disciplines have developed vocabulary and scales to be used in reporting results, they have not become standard practice. This imprecision in vocabulary stems in part from the paucity of research in forensic science and the corresponding limitations in interpreting the results of forensic analyses. Publications such as Evett et al.,5 Aitken and Taroni,6 and Evett7 provide the essential building blocks for the proper assessment and communication of forensic findings.
As a general matter, laboratory reports generated as the result of a scientific analysis should be complete and thorough. They should describe, at a minimum, methods and materials, procedures, results, and conclusions, and they should identify, as appropriate, the sources of uncertainty in the procedures and conclusions along with estimates of their scale (to indicate the level of confidence in the results). Although it is not appropriate and practicable to provide as much detail as might be expected in a research paper, sufficient content should be provided to allow the nonscientist reader to understand what has been done and permit informed, unbiased scrutiny of the conclusion.
Some forensic laboratory reports meet this standard of reporting, but most do not. Some reports contain only identifying and agency information, a brief description of the evidence being submitted, a brief description of the types of analysis requested, and a short statement of the results (e.g., “The green, brown plant material in item #1 was identified as marijuana”). The norm is to have no description of the methods or procedures used, and most reports do not discuss measurement uncertainties or confidence limits. Many disciplines outside the forensic science disciplines have standards, templates, and protocols for data reporting. Although some of the Scientific Working Groups have a scoring system for reporting findings, they are not uniformly or consistently used.
Forensic science reports, and any courtroom testimony stemming from them, must include clear characterizations of the limitations of the analyses, including associated probabilities where possible. Courtroom testimony should be given in lay terms so that all trial participants can understand how to weight and interpret the testimony. In order to enable this, research must be undertaken to evaluate the reliability of the steps of the various identification methods and the confidence intervals associated with the overall conclusions.
I.W. Evett, G. Jackson, J.A. Lambert, and S. McCrossan. 2000. The impact of the principles of evidence interpretation on the structure and content of statements. Science and Justice 40(4):233-239.
C.G.G. Aitken and F. Taroni. 2004. Statistics and the Evaluation of Evidence for ForensicScientists. 2nd ed. V. Barnett, ed. Chichester, UK: John Wiley & Sons Ltd.
I.W. Evett. 1990. The theory of interpreting scientific transfer evidence. Forensic ScienceProgress 4:141-179.