Pevid.rel: Probability of DNA Evidence With the Presence of Relatives

Description Usage Arguments Details Value Author(s) References See Also Examples

Description

Computes probability of DNA evidence, given the proposition about who the contributors to the mixture were. Two main cases are considered: tested suspect (noncontributor) with an unknown relative (contributor), or unknown suspect (contributor) with a tested relative (noncontributor) and two unknown related people as contributors.

Usage

1
Pevid.rel(alleles, prob, x, u = NULL, k = c(1, 0, 0), S = NULL)

Arguments

alleles

vector of distinct alleles (from one specific locus) found in the crime sample.

prob

vector of corresponding allele proportions in a population

x

nonnegative integer. The number of unknown contributors to the mixture.

u

vector of alleles from the mixture, which are not carried by known contributors (and have to be carried by some unknown contributors). If u=NULL (default), all alleles from the crime sample are carried by known contributors.

k

vector of kinship coefficients (k_0, k_1, k_2), where k_i is the probability that two people will share i alleles identical by descent, i = 0, 1, 2.

S

object of class genotype (package genetics), or a string of length 1 with two alleles seperated by '/'. Genotype of the typed person (declared noncontributor) whose untyped relative is assumed to be a contributor to the sample. If S = NULL (default), we consider two related unknown contributors.

Details

Table of kinship coefficients for commonly encountered relationships:

Relationship k_0 k_1 k_2
Parent - child 0 1 0
Grandparent - grandchild 1/2 1/2 0
Full sibs 1/4 1/2 1/4
Halfsibs 1/2 1/2 0
Uncle - nephew 1/2 1/2 0
First cousins 3/4 1/4 0
Second cousins 15/16 1/16 0
Unrelated 1 0 0

The formulas (and their derivations) for the evaluation of the probabilities of DNA evidence with the presence of at most 2 relatives can be found in Hu and Fung (2003).

Value

probability of DNA evidence

Author(s)

Miriam Marusiakova maruskay@gmail.com

The work was supported by the project 1M06014 of the Ministry of Education, Youth and Sports of the Czech Republic.

References

Balding DJ, Nichols RA (1994), DNA profile match probability calculation: how to allow for population stratification, relatedness, database selection and single bands. Forensic Science International 64, 125-140.

Fung WK, Hu YQ (2000), Interpreting DNA mixtures based on the NRC-II recommendation 4.1. Forensic Sci Commun. Available at http://www.fbi.gov/hq/lab/fsc/backissu/oct2000/fung.htm

Hu YQ, Fung WK (2003), Interpreting DNA mixtures with the presence of relatives. International Journal od Legal Medicine 117, 39-45.

Evett IW, Weir BS (1998), Interpreting DNA evidence. Statistical genetics for forensic scientists. Sinauer, Sunderland, MA.

See Also

Pmatch

Examples

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## Rape case in Hong Kong (Fung and Hu (2000))
## mixture (loci: D3S1358, vWA, FGA)
m1 <- c(14, 15, 17, 18)
m2 <- c(16, 18)
m3 <- c(20, 24, 25)
## genotype of the victim (loci: D3S1358, vWA, FGA): 
victim_1 = "15/18"
victim_2 = "18/18"
victim_3 = "20/24"
## genotype of the suspect (loci: D3S1358, vWA, FGA):
suspect_1 = "14/17"
suspect_2 = "16/16"
suspect_3 = "25/25"
## allele proportions 
p1 <- c(0.033, 0.331, 0.239, 0.056)
p2 <- c(0.155, 0.158)
p3 <- c(0.042, 0.166, 0.106)
##
## Likelihood ratio for DNA evidence:
## Prosecution proposition: 
## Contributors were the victim and the suspect.
## Defence proposition 1: 
## Contributors were the victim and one relative of the suspect (sibling).
print(LR11 <- 1 / Pevid.rel(alleles = m1, prob = p1, x = 1, 
  k = c(1/4, 1/2, 1/4), S = suspect_1, u = c(14, 17)))
print(LR12 <- 1 / Pevid.rel(alleles = m2, prob = p2, x = 1, 
  k = c(1/4, 1/2, 1/4), S = suspect_2, u = 16))
print(LR13 <- 1 / Pevid.rel(alleles = m3, prob = p3, x = 1, 
  k = c(1/4, 1/2, 1/4), S = suspect_3, u = 25))
##
## Defence proposition 2: 
## Contributors were one relative of the suspect (sibling) and one unknown. 
print(LR21 <- 1 / Pevid.rel(alleles = m1, prob = p1, x = 2, 
  k = c(1/4, 1/2, 1/4), S = suspect_1, u = m1))
print(LR22 <- 1 / Pevid.rel(alleles = m2, prob = p2, x = 2, 
k = c(1/4, 1/2, 1/4), S = suspect_2, u = m2))
print(LR23 <- 1 / Pevid.rel(alleles = m3, prob = p3, x = 2, 
k = c(1/4, 1/2, 1/4), S = suspect_3, u = m3))
##
## Defence proposition 3: 
## Contributors were two related people (siblings).
print(LR31 <- 1 / Pevid.rel(alleles = m1, prob = p1, x = 2, 
k = c(1/4, 1/2, 1/4), u = m1))
print(LR32 <- 1 / Pevid.rel(alleles = m2, prob = p2, x = 2, 
k = c(1/4, 1/2, 1/4), u = m2))
print(LR33 <- 1 / Pevid.rel(alleles = m3, prob = p3, x = 2, 
k = c(1/4, 1/2, 1/4), u = m3))
##
## Likelihood ratios overall:
## for defence proposition 1
LR11*LR12*LR13
## for defence proposition 2
LR21*LR22*LR23
## for defence proposition 3
LR31*LR32*LR33

forensic documentation built on May 2, 2019, 1:52 p.m.

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