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Investigative DNA Databases the Preserve Identification Information

R. David and M.W. Perlin, "Investigative DNA databases that preserve identification information", International Society for Forensic Genetics, Vienna, Austria, 1-Sep-2011.


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A DNA database can link crime scenes to suspects, providing investigative leads. These DNA associations can solve cold cases, track terrorists, and stop criminals before they inflict further harm. However, current government databases do not fully preserve DNA identification information, and cannot maximize public safety.

DNA data is summarized in a genotype. The genotype can be stored on a database, and compared with other genotypes to form a likelihood ratio (LR) match statistic. Data uncertainty, present in most evidence, translates into genotype probability.

Highly informative interpretation uses all the quantitative DNA data, placing higher probability on more likely genotype values. Most evidence, though, is interpreted by qualitative human review, which diffuses probability across infeasible solutions. Since the LR is proportional to the true genotype probability, weaker interpretation methods lead to weaker (or nonexistent) DNA matches.

The weakest DNA interpretation method is RMNE, which thresholds quantitative data into all-or-none qualitative "allele" events. The current DNA databases (including CODIS) use an RMNE allele representation that discards considerable genotype information, losing sensitivity and specificity.

The "probabilistic genotype" representation is part of the new ANSI/NIST-ITL data exchange standard. Unlike allele lists, this database representation can preserve all DNA identification information, and be quantified dynamically into LR match statistics. Every interpretation method has a corresponding genotype probability representation.

ISFG's 2006 mixture guidelines recommend the more informative LR over RMNE. Unfortunately, current databases transform hard won LR genotypes into less informative RMNE alleles. This talk shows how genotype probability can preserve identification information for DNA investigation.