Theta (FST) Correction
Definition
A correction factor applied to allele frequency estimates to account for population sub-structure (the tendency for allele frequencies to differ between sub-populations). Using theta inflates the RMP slightly, making the statistic conservative in favour of the defendant. Typical values range from 0.01 to 0.03 for well-characterised populations.
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...
- 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...
- 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...
- Random Match Probability (RMP)
- The probability that a randomly chosen unrelated person from the relevant population would match the evidence profile by chance. A very small...
- 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...
- 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 Fallacy
- The converse error of inflating the importance of the RMP by arguing that, because many people in the population share the profile,...
- ENFSI DNA Working Group
- The European Network of Forensic Science Institutes DNA Working Group. Coordinates European forensic DNA standards, including the evaluative reporting guidelines adopted by...
- Prior Odds
- The ratio of the probability of the prosecution hypothesis to the probability of the defence hypothesis before the forensic evidence in question...
- SWGDAM
- Scientific Working Group for DNA Analysis Methods; the US body that publishes interpretation guidelines and validation requirements for forensic DNA laboratories operating...
Explained in these topics
- DNA Match Probability CalculationAn adjustment recommended by NRC-II for population substructure. For a heterozygote with alleles a and b from subpopulation with allele frequencies p and q, th...
- Allele Frequencies, Random Match Probability and the Likelihood RatioA correction factor applied to HWE genotype frequency calculations to account for population substructure (non-random mating within subpopulations). Typically...
- The Concept of Random Match ProbabilityA correction factor applied to allele frequency estimates to account for population sub-structure (the tendency for allele frequencies to differ between sub-po...