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Strengthening Forensic Science in the United States: A Path Forward
work under the supervision of an experienced examiner. The completion of a laboratory’s training program in paint analysis can range between 12 to 18 months.106
Scientific Interpretation and Reporting of Results
SWGMAT sets guidelines for this field, but it has not recommended report wording, and there are no set criteria for determining a conclusion, although a range of conclusions may be used to show the significance of the examination results. The strength of a conclusion depends on such variables as the number of layers present, the sample condition, and the type of paint (vehicular or structural). Terms such as “matched,” “indistinguishable,” “consistent,” or “similar” are used along with the properties of the paints that were compared in stating the results of the comparison.
If there are no significant differences in the properties compared, the examiners may conclude that the paint or coating samples could have had a common origin. This does not mean they came from the same source to the exclusion of all others, but rather that they may have originated from the same source or from different sources that were painted or coated in the same manner. As the number of different layers associated increases (e.g., multiple different layers on a repainted surface), it may be concluded that it is unlikely that the questioned paint originated from any source other than that of the known paint.
SWGMAT has suggested forensic paint analysis and comparison guidelines107,108 that discuss the examination procedure and instrumentation options, and ASTM has published the general guidelines.109 However, neither includes report wording suggestions. Additional work should be done to provide standard language for reporting conclusions and sources of uncertainty. Such work has been completed by working groups for other forensic disciplines. Proficiency testing requirements are agreed upon by the predominant accrediting organization, the American Society of Crime Laboratory Directors-Laboratory Accreditation Board (ASCLD/LAB), which requires testing (internal or external) once per calendar year.