Likelihood of DNA evidence conditioned on a given hypothesis

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Description

likEvid allows the calculation of likelihood for a piece of DNA evidence, for any number of replicates, any number of contributors, and when drop-in and drop-out are possible.

Usage

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likEvid(Repliste, T, V, x, theta, prDHet, prDHom, prC, freq)

Arguments

Repliste

vector of alleles present at a given locus for any number of replicates. If there are two replicates, showing alleles 12,13, and 14 respectively, then Repliste should be given as c(12,13,0,14), where the 0 is used as a separator. An empty replicate is simply 0. For example, replicates (12,13) and and one empty replicate must be given as: c(12,14,0,0).

T

vector of genotypes for the known contributors under Hp. Genotype 12/17 should be given as a vector c(12,17) and genotypes 12/17,14/16, should be given as a unique vector: c(12,17,14,16). If T is empty, set to 0.

V

vector of genotypes for the known non-contributors (see References section) under Hp. See T for format.

x

Number of unknown individuals under H. Set to 0 if there are no unknown contributors.

theta

thete correction, value must be taken in [0,1)

prDHet

probability of dropout for heterozygotes. It is possible to assign different values per contributor. In this case, prDHet must be a vector, of length the number of contributors in T + x, and the probabilities must be given in this order. if the probability of dropout for T is d1, and for the unknown is d2, then prDHet=(d1,d2). In case T is not a heterozygote, the given vector must still be of length length(T) +x, but the given value for T does not matter, because it won't be used, the value in prDHom is used instead. This is a bit ad hoc and an improvement is currently under development.

prDHom

probability of dropout for homozygotes. See description ofr argument PrDHom.

prC

probability of drop-in applied per locus

freq

vector of the corresponding allele frequencies of the analysed locus in the target population

Author(s)

Hinda Haned h.haned@nfi.minvenj.nl

References

Gill, P.; Kirkham, A. & Curran, J. LoComatioN: A software tool for the analysis of low copy number DNA profiles Forensic Science International, 2007, 166(2-3), 128-138

Curran, J. M.; Gill, P. & Bill, M. R. Interpretation of repeat measurement DNA evidence allowing for multiple contributors and population substructure Forensic Science International, 2005, 148, 47-53

See Also

LRmixTK

Examples

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#load allele frequencies
library(forensim)
data(ngm)
#create vector of allele frequencies
d10<-ngm$tab$D10
# evaluate the evidence under Hp; contributors are the suspect and one unknown,
# dropout probabilities for the suspect and the unknown are the same: 0.2 for heterozygotes,
# and 0.1 for homozygotes.
likEvid(Repliste=c(12,13,14),T=c(12,13),V=0,x=1,theta=0,prDHet=c(0.2,0.2),
prDHom=c(0.04,0.04),prC=0,
freq=d10)
#  evaluate the evidence under Hd; contributors are two unknown people, the dropout
# probabilities for the unknowns is kept the same under Hd
likEvid(Repliste=c(12,13,14),T=0,V=0,x=2,theta=0,prDHet=c(0.2,0.2),
prDHom=c(0.04,0.04),prC=0,freq=d10)

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