A revised and updated edition of this practical guide to assessing DNA evidence and presenting that evidence in a courtroom setting.

Throughout its history, DNA profiling has been controversial. As some controversies are resolved, ever more sensitive profiling techniques introduce new difficulties for the evaluation of evidential weight. Today, usable DNA profiles can be obtained from just a few cells, but such profiles may be affected by a range of stochastic effects. Faced with noisy evidence, courts and commentators tend to focus on the question of whether the technology is reliable, but this concept is too vague to be useful. What matters is whether the evaluation of evidential weight is meaningful to jurors and fair to defendants, allowing sufficiently for different sources of uncertainty.

This book provides a thorough presentation of the basic theory of evidence evaluation for DNA profiles, and aims to equip forensic scientists with practical tools to allow them to present DNA evidence in court effectively. It will also be useful to lawyers who need to understand the meaning of statements of evidential weight for DNA evidence, and to challenge them.

Requiring little expertise in either statistics or population genetics, Weight-of-Evidence for Forensic DNA Profiles:

• Links population genetics and statistics theory with practical issues surrounding the presentation of evidence in court; e.g. the prosecutor's fallacy, and the formulation and comparison of competing hypotheses.
• Shows how to calculate likelihood ratios from first principles, including a thorough interpretation of adjustments to allow for co-ancestry.
• Provides a self-contained introduction to population genetics relevant to DNA profiles and to the technology of short tandem repeat (STR, or microsatellite)-based profiling.
• Gives an overview of different evaluation software, and their underlying mathematical models, for low-template and degraded DNA profiles.
• Includes fully worked examples, as well as exercises with solutions.