Forensic Data Science Laboratory
Home Training	Continuing Professional Development Workshop Concepts of likelihood-ratio calculation Calibration and validation of likelihood-ratio systems

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Presenter

Prof Geoffrey Stewart Morrison

Target audiences

Forensic science practitioners



Forensic science researchers



Students of forensic science



Lawyers



Judges

Abstract

(This abstract is to be revised.)



This workshop is aimed at participants who already have some familiarity with the likelihood-ratio framework for evaluation of evidence, e.g., to the level covered in our introductory workshop.



The focus of the workshop is on understanding concepts, not on performing calculations.



Part I of the workshop provides a introduction to calculation of likelihood ratios. Participants will gain an understanding of:

specific-source likelihood ratios



common-source likelihood ratios



similarity-score-based likelihood ratios



Part II of the workshop provides an introduction to calibration and validation of forensic-evaluation systems that output likelihood ratios. Participants will gain an understanding of:

the meaning of calibration and validation in relation to likelihood ratios;



requirements for data used for calibration and validation;



the use of statistical models to perform calibration;



the calculation of the log-likelihood-ratio cost (C_llr) as a validation metric; and



the use of Tippett plots to represent validation results and to support (or not) the likelihood-ratio value calculated for the comparison of the items of interest in the case.

Presentation material

Slides (these slides are to be revised)

Comments from past participants

Court Appointed Forensic Advisor: 

I don’t have a background in statistics, but you presented the material in a way that was really easy for me to understand. I can’t thank you enough.

Deputy Director of a National Forensic Laboratory:

The workshop was very well prepared and conducted. Although I have only a basic knowledge of likelihood ratios, you explained everything very clearly. You are most definitely one of the few people who have a great talent to be a very-very good teacher.

About the presenter

Prof Geoffrey Stewart Morrison is Director of the Forensic Data Science Laboratory at Aston University. His past appointments include Scientific Counsel, Office of Legal Affairs, INTERPOL. He is author of 100 refereed and invited publications. In a citation-based ranking, he is ranked in the top 0.35% of scientists in Legal & Forensic Medicine. He is Associate Editor, focusing on forensic inference and statistics, for the peer-reviewed journal Science & Justice. 2019–2025, he was Chair of the British Standards Institutionʼs Forensic Science Committee and was an active contributor to the development of the new international standard for forensic science, ISO 21043. More information about his work can be found at: http://geoff-morrison.net/

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Introduction to the likelihood ratio framework for evaluation of forensic evidence

https://forensic-data-science.net/workshops/LR_calc.html

This webpage is maintained by Geoffrey Stewart Morrison and was last updated 2025-10-17