Related Experiment Video
Updated: Apr 20, 2026

A Psychophysics Paradigm for the Collection and Analysis of Similarity Judgments
Published on: March 1, 2022
A more straightforward derivation of the LR for a database search
Charles E H Berger1, Peter Vergeer2, John S Buckleton3
1Netherlands Forensic Institute, PO Box 24044, 2490 AA The Hague, The Netherlands; Leiden University, Institute for Criminal Law and Criminology, PO Box 9520, 2300 RA Leiden, The Netherlands.
Abstract:
Matching DNA profiles of an accused person and a crime scene trace are one of the most common forms of forensic evidence. A number of years ago the so-called 'DNA controversy' was concerned with how to quantify the value of such evidence. Given its importance, the lack of understanding of such a basic issue was quite surprising and concerning. Deriving the equation for the likelihood ratio of a DNA database match in a much more direct and simple way is the topic of this paper. As it is much easier to follow it is hoped that this derivation will contribute to the understanding.
Related Concept Videos
Odds Ratio
Derivatives of Logarithmic Functions
Expected Frequencies in Goodness-of-Fit Tests
Introduction to the Sign Test
Probability Laws
Sign Test for Matched Pairs
To conduct the sign test, we first calculate the differences in...

