summary.scanoneperm: LOD thresholds from scanone permutation results

In qtl: Tools for Analyzing QTL Experiments

LOD thresholds from scanone permutation results

Description

Print the estimated genome-wide LOD thresholds on the basis of permutation results from scanone (with n.perm > 0).

Usage

## S3 method for class 'scanoneperm'
summary(object, alpha=c(0.05, 0.10),
                    controlAcrossCol=FALSE, ...)

Arguments

object	Output from the function scanone with n.perm > 0.
alpha	Genome-wide significance levels.
controlAcrossCol	If TRUE, control error rate not just across the genome but also across the columns of LOD scores.
...	Ignored at this point.

Details

If there were autosomal data only or scanone was run with perm.Xsp=FALSE, genome-wide LOD thresholds are given; these are the 1-\alpha quantiles of the genome-wide maximum LOD scores from the permutations.

If there were autosomal and X chromosome data and scanone was run with perm.Xsp=TRUE, autosome- and X-chromsome-specific LOD thresholds are given, by the method described in Broman et al. (2006). Let L_A and L_X be total the genetic lengths of the autosomes and X chromosome, respectively, and let L_T = L_A + L_X Then in place of \alpha, we use

\alpha_A = 1 - (1-\alpha)^{L_A/L_T}

as the significance level for the autosomes and

\alpha_X = 1 - (1-\alpha)^{L_X/L_T}

as the significance level for the X chromosome. The result is a list with two matrices, one for the autosomes and one for the X chromosome.

If controlAcrossCol=TRUE, we use a trick to control the error rate not just across the genome but also across the LOD score columns. Namely, we convert each column of permutation results to ranks, and then for each permutation replicate we find the maximum rank across the columns. We then find the appropriate quantile of the maximized ranks, and then backtrack to the corresponding LOD score within each of the columns. See Burrage et al. (2010), right column on page 118.

Value

An object of class summary.scanoneperm, to be printed by print.summary.scanoneperm. If there were X chromosome data and scanone was run with perm.Xsp=TRUE, there are two matrices in the results, for the autosome and X-chromosome LOD thresholds.

Author(s)

Karl W Broman, [e-mail]

References

Broman KW, Sen Ś, Owens SE, Manichaikul A, Southard-Smith EM, Churchill GA (2006) The X chromosome in quantitative trait locus mapping. Genetics, 174, 2151–2158.

Burrage LC, Baskin-Hill AE, Sinasac DS, Singer JB, Croniger CM, Kirby A, Kulbokas EJ, Daly MJ, Lander ES, Broman KW, Nadeau JH (2010) Genetic resistance to diet-induced obesity in chromosome substitution strains of mice. Mamm Genome, 21, 115–129.

Churchill GA, Doerge RW (1994) Empirical threshold values for quantitative trait mapping. Genetics 138, 963–971.

See Also

scanone, summary.scanone, plot.scanoneperm

Examples

data(fake.f2)

fake.f2 <- calc.genoprob(fake.f2, step=2.5)

operm1 <- scanone(fake.f2, n.perm=100, method="hk")
summary(operm1)

operm2 <- scanone(fake.f2, n.perm=100, method="hk", perm.Xsp=TRUE)
summary(operm2)

# Add noise column
fake.f2$pheno$noise <- rnorm(nind(fake.f2))
operm3 <- scanone(fake.f2, pheno.col=c("phenotype", "noise"), n.perm=10, method="hk")
summary(operm3)
summary(operm3, controlAcrossCol=TRUE, alpha=c(0.05, 0.36))

qtl documentation built on Sept. 11, 2024, 5:43 p.m.