Random Match Probability (RMP)
Definition
The probability that a randomly chosen unrelated person from the relevant population would match the evidence profile by chance. A very small RMP makes the evidence rare among the innocent, but it is not the probability that the defendant is innocent. The prosecutor's fallacy most commonly arises when an RMP is misread as an innocence probability.
Related terms
- Likelihood Ratio (LR)
- The ratio of two conditional probabilities: the probability of the observed evidence given the prosecution's hypothesis (same source), divided by the probability...
- Prosecutor's Fallacy
- The error of treating the RMP (or its reciprocal) as the probability that the defendant is innocent, or as the probability that...
- Defence Fallacy
- The converse error of inflating the importance of the RMP by arguing that, because many people in the population share the profile,...
- Evaluative Reporting
- A framework for expressing forensic conclusions in terms of the probability of the evidence given the prosecution hypothesis versus the defence hypothesis...
- Product Rule
- The rule that, under independence, the joint probability of a multi-locus genotype equals the product of the individual locus genotype frequencies. Used...
- Theta (FST) Correction
- A correction factor applied to allele frequency estimates to account for population sub-structure (the tendency for allele frequencies to differ between sub-populations)....
- Bayes' Theorem
- The mathematical rule that relates prior odds, the likelihood ratio, and posterior odds. In the odds form: O(Hp|E) = O(Hp) x LR....
- Hardy-Weinberg Equilibrium (HWE)
- The expected genotype frequency in a large, randomly mating population with no selection, mutation, or migration. Under HWE, the frequency of a...
- Prior Odds
- The ratio of the probability of the prosecution hypothesis to the probability of the defence hypothesis before the forensic evidence in question...
- Prior Probability
- The probability of guilt (or innocence) based on all evidence other than the specific forensic match under consideration. Bayes' theorem requires a...
- Defence Attorney's Fallacy
- The incorrect argument that a large global or national population means many unrelated individuals could share the profile, while ignoring the geographic...
- Defence Proposition (Hd)
- The alternative proposition, typically asserting that someone else is the source (e.g., 'the crime-scene DNA came from an unknown, unrelated person'). It...
Explained in these topics
- Computing Likelihood Ratios: Worked ExamplesThe probability that a randomly chosen, unrelated individual from the relevant population would share the crime-scene DNA profile. The RMP is the denominator w...
- DNA Match Probability CalculationThe probability that a randomly chosen unrelated person from the reference population would share the observed DNA profile by chance. Calculated by multiplying...
- The Likelihood Ratio: Definition and LogicThe probability that a randomly chosen person from the relevant population would produce evidence matching the crime sample. The RMP is the denominator of the...
- How Numbers Enter Forensic ConclusionsThe probability that a randomly selected individual from a reference population would share a particular forensic profile by chance. Used most commonly in DNA...
- Allele Frequencies, Random Match Probability and the Likelihood RatioThe probability that a randomly selected unrelated individual from the relevant population would share the observed DNA profile by chance. Computed as the prod...
- The Concept of Random Match ProbabilityThe probability that a randomly selected, unrelated individual from the reference population shares the same evidence characteristics as the crime-scene sample...
- The Role of Statistics in Evidence EvaluationThe probability that a randomly chosen unrelated person from the reference population would share the observed feature profile. Used in DNA profiling and other...
- The Defence FallacyThe probability that a randomly selected person from the relevant population would by chance produce the same forensic profile as the sample recovered from the...
- The Prosecutor's FallacyThe probability that a randomly chosen unrelated person from the relevant population would match the evidence profile by chance. A very small RMP makes the evi...
- The Transition from Serology to DNA Profiling in Forensic ScienceThe probability that a randomly selected person from the relevant population would share the same DNA profile as the evidence sample. A key metric for communic...