Theta correction (FST or coancestry coefficient)
Definition
A statistical adjustment applied to DNA match probability calculations to account for expected allele-sharing within subpopulations due to substructure. A theta value of 0.01 to 0.03 is commonly applied in forensic practice; higher values are more conservative. Also called the coancestry coefficient or FST.
Related terms
- Allele frequency
- The proportion of a specific allele variant at a given genetic locus in a defined population. Forensic match probability calculations multiply the...
- 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...
- Minimum allele frequency (minimum frequency ceiling)
- A conservative lower bound applied when an allele is absent or very rare in the database, to prevent an artificially inflated match...
- Population substructure
- The condition in which allele frequencies differ systematically between subgroups within a nominally single population. Substructure means that individuals within a subgroup...
- Reference population database
- A curated collection of allele frequencies or feature measurements from a defined population, used to estimate the probability that a randomly chosen...
Explained in
- Population Databases for Forensic StatisticsA statistical adjustment applied to DNA match probability calculations to account for expected allele-sharing within subpopulations due to substructure. A thet...