Modified ACE-V methodology and error rate in bloodstain pattern analysis

The error rate of bloodstain pattern classification, and thereby the reliability of the discipline, has been a subject of consideration in American courts, especially since the 2009 publication of a report from the National Research Council, “Strengthening Forensic Science in the United States: A Path Forward”. While there is substantial research in the field of bloodstain pattern analysis, there have been relatively few published studies into the error rate of Bloodstain Pattern Analysis (BPA). Of the published studies, several critique the lack of an accepted methodology in BPA and none include a technical review step prior to evaluation of error, despite technical review being common practice amongst forensic scientists. This study examined the error rate of pattern classifications by participating bloodstain pattern analysts using a modified version of the ACE-V methodology. Further, the error rate was calculated before and after verification. The ACE-V (analysis, comparison, evaluation, verification) method is a methodology traditionally used by fingerprint examiners which has potential application in the bloodstain community as a methodology for analysis that mandates a technical review of results prior to issuance of reports. A modified version of the methodology (analysis, classification, evaluation, verification) was utilized for this study. Several error rates were calculated and compared, including the classically considered error rate (Type I error) which was determined to be 27.6% before verification and 21.1% after verification. This study confirmed that a verification step (or technical review step) served to reduce Type I classification errors, wherein analysts chose an incorrect classification and failed to include the correct classification. Furthermore, this study demonstrated the adaptability of the ACE-V methodology for use in bloodstain pattern analysis.