The Reliability of Pattern Classification in Bloodstain Pattern Analysis, Part 1: Bloodstain Patterns on Rigid Non‐absorbent Surfaces

Abstract

This study was designed to produce the first baseline measure of reliability in bloodstain pattern classification. A panel of experienced bloodstain pattern analysts examined over 400 spatter patterns on three rigid non-absorbent surfaces. The patterns varied in spatter type and extent. A case summary accompanied each pattern that either contained neutral information, information to suggest the correct pattern (i.e., was positively biasing), or information to suggest an incorrect pattern (i.e., was negatively biasing). Across the variables under examination, 13% of classifications were erroneous. Generally speaking, where the pattern was more difficult to recognize (e.g., limited staining extent or a patterned substrate), analysts became more conservative in their judgment, opting to be inconclusive. Incorrect classifications increased as a function of the negatively biasing contextual information. The implications of the findings for practice are discussed.

The Reliability of Pattern Classification in Bloodstain Pattern Analysis—PART 2: Bloodstain Patterns on Fabric Surfaces,

“…The rate of incorrectly classifying expiration patterns was 16%. This is markedly higher than the classification of the same pattern type on rigid non‐absorbent surfaces , where the rate was 4%. The characteristic features of an expiration pattern—air bubbles and mucus strands—were present on many of the nonabsorbent surfaces , but not always on the absorbent surfaces, which could explain the difference in analysts’ ability to recognize this pattern type on fabric.…”

“…For the pattern types (cast‐off, impact, expiration, satellite stains from dripped blood, and transfer) and the fabric substrates (denim, dress, sweatpants) under investigation, this study has established a baseline‐estimated error rate in the classification of bloodstain patterns on fabric. The error rate for classifications on fabric surfaces was higher than that observed on rigid non‐absorbent surfaces . Although this finding was mainly due to the misclassification of satellite stains from dripped blood, the analysis of bloodstain patterns on fabric surfaces presents some additional challenges.…”

“…The frequency of correct, incorrect, and inconclusive responses did not vary significantly as a function of the three fabric substrates under investigation. In Taylor et al, , inconclusive decisions increased and correct classifications decreased when the target substrate was highly patterned (i.e., chipboard). Within each of the fabric substrates, the colors were light and uniform, which could explain why the pattern of responding remained stable between each.…”

“…We have previously noted that current BPA classification methods involve some measure of reconstruction, which is exacerbated by the mechanism‐focussed terminology of the discipline. There is an argument for the development of a completely new classification method that is based purely on observable and measurable pattern characteristics and is devoid of any mechanistic overtones.…”

“…To further ensure anonymity, an independent third party liaised with study participants. Participation in PART 1: Bloodstain Patterns on Rigid Non‐Absorbent Surfaces did not exclude analysts from participating in this study.…”