Genotype match probability

The chance that an unrelated person from the same population shares a DNA profile, locus by locus and overall. With theta = 0 this is the product rule (p^2 for a homozygote, 2pq for a heterozygote). A positive theta applies the Balding-Nichols correction for shared ancestry. That never makes a homozygote match rarer than the product rule says; it can make a heterozygote match rarer when both alleles are common. See proof("gtmp").

Usage

gtmp(p, q = NULL, hom = FALSE, theta = 0)

Arguments

p

Frequency of the first allele at each locus: numbers above 0 and at most 1, optionally named by locus, as a numeric vector, a 1-d table, a list of single numbers or a one-row data frame.

q

Frequency of the second allele at each locus; not read where hom is TRUE. Named inputs are matched to p by locus name, unnamed ones by position (only names protect against a mismatch).

hom

TRUE where the genotype is homozygous: one value, or one per locus, matched to p by name when both are named.

theta

The coancestry coefficient: one number from 0 up to, not including, 1.

Value

A list: locus, a data frame with locus, hom and mp; log10mp, the base-10 logarithm of the profile match probability; and log10lr, the same with the sign changed, the weight of a single-source match against an unrelated alternative.

References

Balding, D. J. and Nichols, R. A. (1994). DNA profile match probability calculation. Forensic Science International, 64(2-3), 125-140. doi:10.1016/0379-0738(94)90222-4

Examples

gtmp(p = c(D3 = 0.1, vWA = 0.2), q = c(0.3, NA), hom = c(FALSE, TRUE),
     theta = 0.03)
#> $locus
#>   locus   hom         mp
#> 1    D3 FALSE 0.07467851
#> 2   vWA  TRUE 0.06607071
#> 
#> $log10mp
#> [1] -2.306795
#> 
#> $log10lr
#> [1] 2.306795
#>