DNA Probabilities in People v. Prince: When are racial and ethnic statistics relevant?

TL;DR

This paper critiques the exclusive use of racial and ethnic DNA statistics in court cases, proposing a logical framework for broader racial considerations and alternative ways to quantify DNA match evidence.

Contribution

It provides a logical justification for considering multiple races in DNA evidence and discusses methods to quantify match strength without racial statistics.

Findings

Likelihood-based reasoning supports multi-race DNA evidence

Problems with the one-race-only rule are identified

Alternative quantitative expressions for DNA match probative value are discussed

Abstract

When a defendant's DNA matches a sample found at a crime scene, how compelling is the match? To answer this question, DNA analysts typically use relative frequencies, random-match probabilities or likelihood ratios. They compute these quantities for the major racial or ethnic groups in the United States, supplying prosecutors with such mind-boggling figures as ``one in nine hundred and fifty sextillion African Americans, one in one hundred and thirty septillion Caucasians, and one in nine hundred and thirty sextillion Hispanics." In People v. Prince, a California Court of Appeals rejected this practice on the theory that only the perpetrator's race is relevant to the crime; hence, it is impermissible to introduce statistics about other races. This paper critiques this reasoning. Relying on the concept of likelihood, it presents a logical justification for referring to a range of races and identifies some problems with the one-race-only rule. The paper also notes some ways to express the probative value of a DNA match quantitatively without referring to variations in DNA profile frequencies among races or ethnic groups.