Study Reports Error Rates for Bloodstain Pattern Analysis

• NCJ Number: 304103
• Date Published: February 2022
• Grant Number(s): 2018-DU-BX-0214
• Agencies: NIJ
• Publication Type: Research (Applied/Empirical)
• Award: Black Box Evaluation of Bloodstain Pattern Analysis Conclusions

Annotation

In this project supported by the National Institute of Justice, 75 practicing bloodstain pattern analysts were asked to respond to classification prompts or questions about bloodstains.

Abstract

Forensic practitioners known as bloodstain pattern analysts seek to answer questions about the manner and sequence of events of a crime by examining the bloodstains left behind. Their methods are largely based on subjective expert opinion. In this project supported by the National Institute of Justice, 75 practicing bloodstain pattern analysts were asked to respond to classification prompts or questions about bloodstains. The researchers then examined how often the analysts’ conclusions matched the known cause. They found that, on average, about 11% of the time the analysts’ conclusions were wrong. And although the average group response as a whole was seldom wrong, any two analysts’ conclusions contradicted each other at an overall rate of about 8%. However, when focusing specifically on erroneous responses, those same errors were reproduced by a second analyst from 18% to 34% of the time. Those rates are particularly concerning because technical review of operational casework by a second analyst is a common method intended to prevent errors.