snpgdsIBDMLELogLik {SNPRelate} | R Documentation

## Log likelihood for MLE method in the Identity-By-Descent (IBD) Analysis

### Description

Calculate the log likelihood values from maximum likelihood estimation.

### Usage

    snpgdsIBDMLELogLik(gdsobj, ibdobj, k0 = NaN, k1 = NaN,
        relatedness=c("", "self", "fullsib", "offspring",
        "halfsib", "cousin", "unrelated"))

### Arguments

`gdsobj` | an object of class `SNPGDSFileClass`, a SNP GDS file
`ibdobj` | the `snpgdsIBDClass` object returned from snpgdsIBDMLE
`k0` | specified IBD coefficient
`k1` | specified IBD coefficient
`relatedness` | specify a relatedness, otherwise use the values of k0 and k1

### Details

If (`relatedness` == "") and (k0 == NaN or k1 == NaN), then return the log likelihood values for each (k0, k1) stored in ibdobj. \ If (`relatedness` == "") and (k0 != NaN) and (k1 != NaN), then return the log likelihood values for a specific IBD coefficient (k0, k1). \ If `relatedness` is: "self", then k0 = 0, k1 = 0; "fullsib", then k0 = 0.25, k1 = 0.5; "offspring", then k0 = 0, k1 = 1; "halfsib", then k0 = 0.5, k1 = 0.5; "cousin", then k0 = 0.75, k1 = 0.25; "unrelated", then k0 = 1, k1 = 0.

### Value

Return a n-by-n matrix of log likelihood values, where n is the number of samples.

### Author(s)

Xiuwen Zheng

### References

Milligan BG. 2003. Maximum-likelihood estimation of relatedness. Genetics 163:1153-1167.

Weir BS, Anderson AD, Hepler AB. 2006. Genetic relatedness analysis: modern data and new challenges. Nat Rev Genet. 7(10):771-80.

Choi Y, Wijsman EM, Weir BS. 2009. Case-control association testing in the presence of unknown relationships. Genet Epidemiol 33(8):668-78.

### See Also

`snpgdsIBDMLE`, `snpgdsIBDMoM`

### Examples

    # open an example dataset (HapMap)
    genofile <- snpgdsOpen(snpgdsExampleFileName())

    YRI.id <- read.gdsn(index.gdsn(genofile, "sample.id"))[
        read.gdsn(index.gdsn(genofile, "sample.annot/pop.group"))=="YRI"]
    YRI.id <- YRI.id[1:30]

    # SNP pruning
    set.seed(10)
    snpset <- snpgdsLDpruning(genofile, sample.id=YRI.id, maf=0.05,
        missing.rate=0.05)
    snpset <- sample(unlist(snpset), 250)
    mibd <- snpgdsIBDMLE(genofile, sample.id=YRI.id, snp.id=snpset)
    names(mibd)

    # select a set of pairs of individuals
    d <- snpgdsIBDSelection(mibd, kinship.cutoff=1/8)
    head(d)

    # log likelihood

    loglik <- snpgdsIBDMLELogLik(genofile, mibd)
    loglik0 <- snpgdsIBDMLELogLik(genofile, mibd, relatedness="unrelated")

    # likelihood ratio test
    p.value <- pchisq(loglik - loglik0, 1, lower.tail=FALSE)

    flag <- lower.tri(mibd$k0)
    plot(NaN, xlim=c(0,1), ylim=c(0,1), xlab="k0", ylab="k1")
    lines(c(0,1), c(1,0), col="red", lty=3)
    points(mibd$k0[flag], mibd$k1[flag])

    # specify the allele frequencies
    afreq <- snpgdsSNPRateFreq(genofile, sample.id=YRI.id,
        snp.id=snpset)$AlleleFreq
    subibd <- snpgdsIBDMLE(genofile, sample.id=YRI.id[1:25], snp.id=snpset,
        allele.freq=afreq)
    summary(c(subibd$k0 - mibd$k0[1:25, 1:25]))
    # ZERO
    summary(c(subibd$k1 - mibd$k1[1:25, 1:25]))
    # ZERO

    # close the genotype file
    snpgdsClose(genofile)

[Package SNPRelate version 1.18.1 Index]