Evaluating and Presenting DNA evidence
- Created by: AAntonianannetti
- Created on: 10-05-19 14:25
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- Evaluating and presenting DNA evidence
- Final stage in a criminal case
- Match probabilities
- Should be evaluated and reported correctly so that they do not mislead the jury.
- DNA evidence only assists in determining the most likely source of biological evidence
- Likelihood ratios
- The Bayesian Approach
- The Frequentist Approach
- The profile frequency is presented as a random match probability, which can be taken as the reciprocal of the profile frequency
- When using the several loci, the product rule gives match probabilities of hundreds of billions.
- In the UK, the ceiling principle is applied - 1 in a billion
- expresses the probability that a person, selected at random, has the same profile as the evidence.
- Advantages
- Straightforward
- Easily understood
- Disadvantages
- Does not consider two propositions
- Not very scientific
- When using the several loci, the product rule gives match probabilities of hundreds of billions.
- Random Match Probability = 1/profile frequency
- The profile frequency is presented as a random match probability, which can be taken as the reciprocal of the profile frequency
- The two fallacies
- Defendants Fallacy
- Assumes that every person with a matching profile has equal chances of being guilty.
- Prosecutors Fallacy
- Assumes that there a low probability of false matches does not mean a low probability of some false matches being found
- Two errors can be made if the wording is wrong
- Defendants Fallacy
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