DNAmix 2021: Laboratory policies, procedures, and casework scenarios summary and dataset

Area of Science:

• Forensic Science
• Genetics
• Molecular Biology

Background:

• Forensic DNA mixture interpretation is complex, with potential for variability.
• Standardized interpretation guidelines are crucial for consistent and reliable results.
• Previous studies indicated variability, necessitating large-scale investigations.

Purpose of the Study:

• To assess consistency and variation in forensic DNA mixture interpretation among laboratories.
• To identify sources of variability in DNA mixture analysis.
• To characterize laboratory policies and standard operating procedures (SOPs) related to DNA mixture interpretation.

Main Methods:

• A multi-phasic study involving questionnaires for participating laboratories.
• Collected data on laboratory policies, SOPs, DNA workflows, and systems.
• Administered a Policies & Procedures (P&P) Questionnaire and a Casework Scenarios Questionnaire (CSQ).

Main Results:

• Documented variation in policies and SOPs across 86 forensic laboratories.
• Detailed variations in suitability assessments, contributor number estimations, and statistical analyses.
• Provided insights into case-scenario specific decisions and mixture casework for 83 laboratories.

Conclusions:

• The study provides a snapshot of forensic DNA mixture interpretation practices in 2021-2022.
• Identified significant variability in policies and procedures, impacting casework consistency.
• Emphasizes the need for further standardization in forensic DNA mixture analysis.