Choice of population database for forensic DNA profile analysis

Area of Science:

• Forensic Science
• Population Genetics
• Statistical Analysis

Background:

• Evaluating the weight of evidence (WoE) for DNA contributors requires allele frequency databases.
• Current practice involves extensive calculations using multiple population databases, which is impractical for complex profiles.
• Reporting the most conservative WoE is standard, favoring the defense.

Purpose of the Study:

• To propose and investigate a more efficient heuristic for calculating the weight of evidence in DNA analysis.
• To assess the conservativeness of using a single, best-matched ancestral database with an FST adjustment.
• To compare the proposed heuristic with traditional multi-database approaches.

Main Methods:

• Simulated one- and two-contributor DNA profiles using five population databases.
• Applied a heuristic rule: using the best ancestral match database with an FST adjustment (FST=0.03).
• Compared the heuristic's WoE calculations against multiple alternative database calculations.

Main Results:

• The proposed heuristic yielded WoE values more favorable to the defense in over 99% of comparisons.
• The average difference in WoE per locus was approximately 0.2 bans (orders of magnitude).
• The degree of conservativeness can be adjusted by modifying the FST value.

Conclusions:

• The heuristic offers a practical and efficient method for DNA profile WoE calculations.
• It provides a flexible level of conservativeness suitable for forensic applications.
• This approach simplifies complex analyses while maintaining robust evidential value.