Description Usage Arguments Details Value Author(s) References See Also Examples
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.
1 |
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 |
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 |
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).
probability of DNA evidence
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.
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.
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 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | ## 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
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