# expectedLR: Expected likelihood ratio In forrel: Forensic Pedigree Analysis and Relatedness Inference

## Description

This function computes the expected LR for a single marker, in a kinship test comparing two hypothesised relationships between a set of individuals. The true relationship may differ from both hypotheses. Some individuals may already be genotyped, while others are available for typing. The implementation uses `oneMarkerDistribution()` to find the joint genotype distribution for the available individuals, conditional on the known data, in each pedigree.

## Usage

 `1` ```expectedLR(numeratorPed, denominatorPed, truePed = numeratorPed, ids, marker) ```

## Arguments

 `numeratorPed` A `ped` object. `denominatorPed` A `ped` object. `truePed` A `ped` object. `ids` A vector of ID labels corresponding to untyped pedigree members. (These must be members of all three input pedigrees). `marker` either a marker object compatible with `numeratorPed`, or the name or index of a marker attached to `numeratorPed`.

## Value

A positive number.

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25``` ```#--------- # Curious example showing that ELR may decrease # by typing additional reference individuals #--------- # Numerator ped numPed = nuclearPed(father = "fa", mother = "mo", child = "ch") # Denominator ped: fa, mo, ch are unrelated. Ugly hack! denomPed = nuclearPed(father = "fa", mother = "mo", nch = 1) denomPed = addChildren(denomPed, father = "ch", mother = "mo", nch = 1) # Scenario 1: Only mother is typed; genotype 1/2 p = 0.9 m1 = marker(numPed, mo = 1:2, afreq = c("1" = p, "2" = 1-p)) expectedLR(numPed, denomPed, ids = "ch", marker = m1) 1/(8*p*(1-p)) + 1/2 # exact formula # Scenario 2: Include father, with genotype 1/1 m2 = m1 genotype(m2, id = "fa") = c(1, 1) expectedLR(numPed, denomPed, ids = "ch", marker = m2) 1/(8*p*(1-p)) + 1/(4*p^2) # exact formula ```

forrel documentation built on March 14, 2021, 1:06 a.m.