standardScreeningBinaryTrait {WGCNA}

Standard screening for binatry traits

Description

The function standardScreeningBinaryTrait computes widely used statistics for relating the columns of the input data frame (argument datE) to a binary sample trait (argument y). The statistics include Student t-test p-value and the corresponding local false discovery rate (known as q-value, Storey et al 2004), the fold change, the area under the ROC curve (also known as C-index), mean values etc. If the input option KruskalTest is set to TRUE, it also computes the Kruskal Wallist test p-value and corresponding q-value. The Kruskal Wallis test is a non-parametric, rank-based group comparison test.

Usage

standardScreeningBinaryTrait(
     datExpr, y, 
     corFnc = cor, corOptions = list(use = 'p'),
     kruskalTest = FALSE, qValues = FALSE,
     var.equal=FALSE, na.action="na.exclude",
     getAreaUnderROC = TRUE)

Arguments

datExpr

a data frame or matrix whose columns will be related to the binary trait

y

a binary vector whose length (number of components) equals the number of rows of datE

corFnc

correlation function. Defaults to Pearson correlation.

corOptions

a list specifying options to corFnc. An empty list must be specified as list() (supplying NULL instead will trigger an error).

kruskalTest

logical: should the Kruskal test be performed?

qValues

logical: should the q-values be calculated?

var.equal

logical input parameter for the Student t-test. It indicates whether to treat the two variances (corresponding to the binary grouping) are being equal. If TRUE then the pooled variance is used to estimate the variance otherwise the Welch (or Satterthwaite) approximation to the degrees of freedom is used. Warning: here the default value is TRUE which is different from the default value of t.test. Type help(t.test) for more details.

na.action

character string for the Student t-test: indicates what should happen when the data contain missing values NAs.

getAreaUnderROC

logical: should area under the ROC curve be calculated? The calculation slows the function down somewhat.

Value

A data frame whose rows correspond to the columns of datE and whose columns report

ID

column names of the input datExpr.

corPearson

pearson correlation with a binary numeric version of the input variable. The numeric variable equals 1 for level 1 and 2 for level 2. The levels are given by levels(factor(y)).

t.Student

Student's t-test statistic

pvalueStudent

two-sided Student t-test p-value.

qvalueStudent

(if input qValues==TRUE) q-value (local false discovery rate) based on the Student T-test p-value (Storey et al 2004).

foldChange

a (signed) ratio of mean values. If the mean in the first group (corresponding to level 1) is larger than that of the second group, it equals meanFirstGroup/meanSecondGroup. But if the mean of the second group is larger than that of the first group it equals -meanSecondGroup/meanFirstGroup (notice the minus sign).

meanFirstGroup

means of columns in input datExpr across samples in the first group.

meanSecondGroup

means of columns in input datExpr across samples in the second group.

SE.FirstGroup

standard errors of columns in input datExpr across samples in the first group. Recall that SE(x)=sqrt(var(x)/n) where n is the number of non-missing values of x.

SE.SecondGroup

standard errors of columns in input datExpr across samples in the second group.

areaUnderROC

the area under the ROC, also known as the concordance index or C.index. This is a measure of discriminatory power. The measure lies between 0 and 1 where 0.5 indicates no discriminatory power. 0 indicates that the "opposite" predictor has perfect discriminatory power. To compute it we use the function rcorr.cens with outx=TRUE (from Frank Harrel's package Hmisc). Only present if input getAreUnderROC is TRUE.

nPresentSamples

number of samples with finite measurements for each gene.

If input kruskalTest is TRUE, the following columns further summarize results of Kruskal-Wallis test:

stat.Kruskal

Kruskal-Wallis test statistic.

stat.Kruskal.signed

(Warning: experimental) Kruskal-Wallis test statistic including a sign that indicates whether the average rank is higher in second group (positive) or first group (negative).

pvaluekruskal

Kruskal-Wallis test p-values.

qkruskal

q-values corresponding to the Kruskal-Wallis test p-value (if input qValues==TRUE).

Author(s)

Steve Horvath

References

Storey JD, Taylor JE, and Siegmund D. (2004) Strong control, conservative point estimation, and simultaneous conservative consistency of false discovery rates: A unified approach. Journal of the Royal Statistical Society, Series B, 66: 187-205.

Examples

require(survival) # For is.Surv in rcorr.cens
m=50
y=sample(c(1,2),m,replace=TRUE)
datExprSignal=simulateModule(scale(y),30)
datExprNoise=simulateModule(rnorm(m),150)
datExpr=data.frame(datExprSignal,datExprNoise)

Result1=standardScreeningBinaryTrait(datExpr,y)
Result1[1:5,]



# use unequal variances and calculate q-values
Result2=standardScreeningBinaryTrait(datExpr,y, var.equal=FALSE,qValue=TRUE)
Result2[1:5,]

# calculate Kruskal Wallis test and q-values
Result3=standardScreeningBinaryTrait(datExpr,y,kruskalTest=TRUE,qValue=TRUE)
Result3[1:5,]