Sibling Likelihood Ratio (SLR)
Definition
Likelihood ratio comparing the probability of the observed genotype data if two persons are full siblings versus unrelated. Values much greater than 1 support sibship; values less than 1 support non-sibship.
- Compares
- Full-sibling hypothesis versus unrelated hypothesis
- SLR much greater than 1
- Supports sibship
- SLR less than 1
- Supports non-sibship
- Common application
- Missing-persons identification when a parent sample is unavailable
Common questions
Why is the sibling likelihood ratio used instead of a standard paternity index in missing-persons work?+
A paternity or parentage index needs a parent's genetic profile, which is often unavailable in missing-persons cases; the SLR instead compares two potential siblings directly, letting investigators evaluate a claimed sibling relationship using only samples from the two people being compared and a reference population.
Is a full-sibling relationship as easy to confirm genetically as a parent-child relationship?+
No, it is generally harder. Full siblings share on average half their DNA, similar to a parent-child pair, but the exact amount shared varies randomly between sibling pairs due to independent assortment, so sibling likelihood ratios tend to be less conclusive than parentage indices and often need more loci to reach a comparable strength of evidence.
Related terms
- Combined Paternity Index (CPI)
- The product of all individual paternity indices across all marker systems tested. Assumes independence of the marker systems. The CPI is a...
- Duo / Motherless Case
- A paternity test in which the mother's profile is unavailable; the PI denominator must integrate over all possible maternal allele contributions from...
- Familias
- Open-source kinship LR software developed in Norway, the reference platform for ISFG kinship workshops and used operationally by forensic labs in Sweden,...
- Inbreeding Coefficient (F)
- The probability that two alleles at a locus in an individual are identical by descent, reflecting population consanguinity. Non-zero F values affect...
- NamUs
- National Missing and Unidentified Persons System (US), a national database cross-matching PM profiles of unidentified remains against AM kinship reference profiles; has...
- Paternity Index (PI)
- A likelihood ratio that compares the probability of the observed serological profile if the alleged father is the biological father to the...
- Track Child
- India's Missing Persons and Children portal managed by the Ministry of Women and Child Development and NCRB, the domestic framework through which...