Calculates match probability of the genotype of the suspect and that of the crime stain
presumed to have come from an offender other than the suspect.
Possible assumptions: the suspect and an unknown offender are unrelated, or are members of
the same subpopulation with a given coancestry coefficient, or are close relatives.
Usage
Pmatch(prob, k = c(1, 0, 0), theta = 0)
Arguments
prob
matrix with 2 rows and L columns (L is the number of loci, each locus has
2 alleles). Contains frequencies of alleles in a population found in the crime stain.
For homozygous locus just one entry is nonzero. prob can also be a vector with
odd number of elements (it is then easily transformed to a matrix with
two rows, the matrix is filled by columns)
k
vector of kinship coefficients (k_0, k_1, k_2), where
k_i is the probability that two people (the suspect and an unknown offender)
will share i alleles identical by descent, i = 0, 1, 2.
theta
number from the interval [0,1). Coancestry coefficient
theta describes variation in allele proportions among subpopulations.
Default is 0 (no variation, whole population in Hardy-Weinberg equilibrium).
The recommended values of theta are 0.01 for large
subpopulations such as USA, and 0.03 for small isolated subpopulations
(National Research Council, 1996).
If theta is nonzero, the allele proportions are taken from the
whole population (not from the subpopulation).
Details
The match probability is calculated as
k_2 + k_1 Z_1 + k_0 Z_2,
where
k_0, k_1, k_2 are the kinship coefficients (for more information see
Details of Pevid.rel),
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.
Evett IW, Weir BS (1998), Interpreting DNA evidence;
Statistical genetics for forensic scientists. Sinauer, Sunderland, MA.
National Research Council (1996), The evaluation of forensic DNA evidence
National Academy Press, Washington, DC.
See Also
Pevid.rel, Pevid.gen
Examples
## match probability of thirteen-locus genotype
## (11 heterozygous and 2 homozygous loci)
p<-c(0.057,0.160,0.024,0.122,0.078,0.055,0.035,0.150,
0.195,0.027,0.084,0.061,0.122,0.083,0.164,0.065,0.143,
0.151,0.167,0.180,0.099,0.182,0.120,0,0.182,0)
## suspect and offender are unrelated
Pmatch(p)
## suspect and offender are unrelated but members of the same
## subpopulation with the coancestry coefficient theta
Pmatch(p, theta = 0.03)
## suspect and offender are close relatives (cousins)
Pmatch(p, k = c(3/4, 1/4, 0))
## suspect and offender are close relatives (cousins) and
## members of the same subpopulation with the coancestry
## coefficient theta
Pmatch(p, k = c(3/4, 1/4, 0), theta = 0.03)
##
## one locus
Pmatch(p[1:2], theta = 0.03)
Pmatch(p[25:26], theta = 0.03)
## compare
Pevid.gen(alleles = c(1, 2), prob = p[1:2], V = "1/2", x = 1,
theta = 0.03)
Pevid.gen(alleles = "a", prob = p[25], V = "a/a", x = 1,
theta = 0.03)