The influence of relatives on the efficiency and error rate of familial searching

TL;DR

This study evaluates the effectiveness and risks of California's familial search protocol using simulations, revealing high accuracy for close relatives but significant misidentification risks for distant relatives, especially affecting overrepresented ethnic groups.

Contribution

It provides a detailed simulation-based analysis of the California familial search protocol, highlighting its accuracy for close relatives and potential for misidentification of distant relatives, with implications for privacy and fairness.

Findings

High probability (80-99%) of identifying first-degree relatives.

Low probability of false positives for unrelated individuals.

Significant risk of misidentifying distant relatives as close relatives.

Abstract

We investigate the consequences of adopting the criteria used by the state of California, as described by Myers et al. (2011), for conducting familial searches. We carried out a simulation study of randomly generated profiles of related and unrelated individuals with 13-locus CODIS genotypes and YFiler Y-chromosome haplotypes, on which the Myers protocol for relative identification was carried out. For Y-chromosome sharing first degree relatives, the Myers protocol has a high probability (80 - 99%) of identifying their relationship. For unrelated individuals, there is a low probability that an unrelated person in the database will be identified as a first-degree relative. For more distant Y-haplotype sharing relatives (half-siblings, first cousins, half-first cousins or second cousins) there is a substantial probability that the more distant relative will be incorrectly identified as a first-degree relative. For example, there is a 3 - 18% probability that a first cousin will be identified as a full sibling, with the probability depending on the population background. Although the California familial search policy is likely to identify a first degree relative if his profile is in the database, and it poses little risk of falsely identifying an unrelated individual in a database as a first-degree relative, there is a substantial risk of falsely identifying a more distant Y-haplotype sharing relative in the database as a first-degree relative, with the consequence that their immediate family may become the target for further investigation. This risk falls disproportionately on those ethnic groups that are currently overrepresented in state and federal databases.