The Interpretation of DNA Evidence: A Case Study in Probabilities
National Academies of Science, Engineering and Medicine, Science Policy Decision-making Educational Modules, 2016
65 Pages Posted: 27 Jul 2016 Last revised: 2 Sep 2016
Date Written: June 16, 2016
This educational module on DNA evidence commissioned by a committee of the National Academies presents trial testimony, exhibits, and opinions in a case in which federal courts at every level discerned “inaccuracies” in the testimony of a leading expert about probabilities associated with the DNA evidence. By embedding these legal materials in background explanations, critical questions, and short problems, the module supports self-study and class discussions that can elucidate key principles in scientific reasoning and quantitative analysis and that can help students understand conditional probabilities.
The module includes information and exercises relating to the following scientific and statistical principles and skills: (1) sampling (defining a relevant population, spotting sources of bias and uncertainty, and interpreting confidence intervals); (2) modeling DNA profile probabilities (testing assumptions and sensitivity analysis); and (3) probability theory (the concept of mathematical probability, probabilities of events such as a DNA match to a randomly selected individual, independent and dependent events, conditional probability and the transposed conditional, likelihood ratios for pairs of hypotheses as a measure of the probative value of DNA matches and other scientific test results, and Bayes’ rule for deducing a posterior probability from a likelihood ratio and a prior probability).
Keywords: DNA Evidence, Probability, Probative Value, Sampling
JEL Classification: C11, C13, C19
Suggested Citation: Suggested Citation