Weight of evidence of Y-STR matches computed with the discrete Laplace method: Impact of adding a suspect’s profile to a reference database

Mikkel Meyer Andersen*, Svante Eriksen, Niels Morling

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The discrete Laplace method is recommended by multiple parties (including the International Society for Forensic Genetics, ISFG) to estimate the weight of evidence in criminal cases when a suspect's Y-STR profile matches the crime scene Y-STR profile. Unfortunately, modelling the distribution of Y-STR profiles in the population reference database is time-consuming and requires expert knowledge. When the suspect's Y-STR profile is added to the database, as would be the protocol in many cases, the parameters of the discrete Laplace model must be re-estimated. We found that the likelihood ratios with and without adding the suspect's Y-STR profile were almost identical with 1,000 or more Y-STR profiles in the database for Y-STR profiles with 8, 12, and 17 loci. Thus, likelihood ratio calculations can be performed in seconds if an established discrete Laplace model based on at least 1,000 Y-STR profiles is used. A match in a population reference database with 17 Y-STR loci from at least 1,000 male individuals results in a likelihood ratio above 10,000 in approximately 94% of the cases, and above 100,000 in approximately 82% of the cases. We offer free software accessible without restrictions to estimate a discrete Laplace model using a Y-STR reference database and subsequently to calculate likelihood ratios.

Original languageEnglish
Article number102839
JournalForensic Science International: Genetics
Volume64
ISSN1872-4973
DOIs
Publication statusPublished - May 2023

Keywords

  • Discrete Laplace
  • Forensic genetics
  • Weight of evidence
  • Y-STR
  • Y-chromosome

Fingerprint

Dive into the research topics of 'Weight of evidence of Y-STR matches computed with the discrete Laplace method: Impact of adding a suspect’s profile to a reference database'. Together they form a unique fingerprint.

Cite this