setMeanVarCurve {MAnorm2}

Set the Mean-Variance Curve of a Set of bioCond Objects

Description

Given a set of bioCond objects, setMeanVarCurve associates a common mean-variance curve with each of them, assesses the overall goodness of fit by estimating the number of prior degrees of freedom, and accordingly estimates their variance ratio factors (see also fitMeanVarCurve).

Usage

setMeanVarCurve(
  conds,
  predict,
  occupy.only = TRUE,
  method = "NA",
  ratio.var = estimateVarRatio(conds),
  .call = NULL
)

Arguments

conds

A list of bioCond objects, of which at least one should contain replicate samples.

predict

A function representing the mean-variance curve to be associated with the bioConds. It should accept a vector of means and return the predicted variances.

occupy.only

A logical scalar. If it is TRUE (default), only occupied intervals are used to estimate the number of prior degrees of freedom and the variance ratio factors. Otherwise, all intervals are used.

method

A character string giving the method for fitting the mean-variance curve. Used only for constructing the fit.info fields (see "Value" below).

ratio.var

Backup variance ratio factors of the bioConds. Only used when the estimated number of prior degrees of freedom is 0, which in practice rarely happens.

.call

Never care about this argument.

Details

The specific behavior of this function is pretty much the same as fitMeanVarCurve, except that the mean-variance curve is directly specified by users rather than fitted based on the observed means and variances. Refer to fitMeanVarCurve for a detailed description of related terms.

Interestingly, if a positive constant function is supplied as the mean-variance curve, the resulting statistical model will be rather similar to the one implemented in the limma package (see also "References"). Notably, using a constant function as the mean-variance curve is particularly suited to bioCond objects that have gone through a variance-stabilizing transformation (see vstBioCond for details and "Examples" below) as well as bioConds whose structure matrices have been specifically designed (see "References").

Value

setMeanVarCurve returns the argument list of bioCond objects, each of which has an added (updated) fit.info field constructed based on the supplied mean-variance curve. The field is itself a list consisting of the following components:

calls

The two function calls for associating a mean variance curve with this bioCond and estimating the related parameters, respectively. The latter is only present if you have made an explicit call to some function (e.g., estimatePriorDf) for performing the parameter estimation.

method

Method used for fitting the mean-variance curve.

predict

The supplied mean-variance function.

mvcID

ID of the mean-variance curve.

df.prior

Number of prior degrees of freedom assessing the goodness of fit of the mean-variance curve.

ratio.var

Variance ratio factor of this bioCond.

Each bioCond object in the returned list has the same values of all these components but the ratio.var. mvcID is automatically generated by the function to label the supplied mean-variance curve. Each call to setMeanVarCurve results in a unique mvcID.

Besides, if there exist bioCond objects that contain only one ChIP-seq sample, an attribute named "no.rep.rv" will be added to the returned list, recording the variance ratio factor of no-replicate conditions.

References

Smyth, G.K., Linear models and empirical bayes methods for assessing differential expression in microarray experiments. Stat Appl Genet Mol Biol, 2004. 3: p. Article3.

Law, C.W., et al., voom: Precision weights unlock linear model analysis tools for RNA-seq read counts. Genome Biol, 2014. 15(2): p. R29.

Tu, S., et al., MAnorm2 for quantitatively comparing groups of ChIP-seq samples. Genome Res, 2021. 31(1): p. 131-145.

See Also

bioCond for creating a bioCond object from a set of ChIP-seq samples; fitMeanVarCurve for fitting a mean-variance curve for a set of bioCond objects; estimateVarRatio for estimating the relative variance ratio factors of a set of bioConds; varRatio for a formal description of variance ratio factor; estimatePriorDf for estimating the number of prior degrees of freedom and the corresponding variance ratio factors; estimatePriorDfRobust for a robust version of estimatePriorDf.

Examples

data(H3K27Ac, package = "MAnorm2")
attr(H3K27Ac, "metaInfo")

## Perform differential analysis on bioConds that have gone through a
## variance-stabilizing transformation.

# Perform MA normalization and construct bioConds to represent cell lines
# (i.e., individuals).
norm <- normalize(H3K27Ac, 4, 9)
norm <- normalize(norm, 5:6, 10:11)
norm <- normalize(norm, 7:8, 12:13)
conds <- list(GM12890 = bioCond(norm[4], norm[9], name = "GM12890"),
              GM12891 = bioCond(norm[5:6], norm[10:11], name = "GM12891"),
              GM12892 = bioCond(norm[7:8], norm[12:13], name = "GM12892"))
autosome <- !(H3K27Ac$chrom %in% c("chrX", "chrY"))
conds <- normBioCond(conds, common.peak.regions = autosome)

# Fit a mean-variance curve.
conds <- fitMeanVarCurve(conds, method = "parametric", occupy.only = TRUE)
plotMeanVarCurve(conds, subset = "occupied")

# Apply a variance-stabilizing transformation.
vst_conds <- list(GM12890 = vstBioCond(conds$GM12890))
vst.func <- attr(vst_conds$GM12890, "vst.func")
temp <- matrix(vst.func(as.numeric(conds$GM12891$norm.signal)),
               nrow = nrow(norm))
vst_conds$GM12891 <- bioCond(temp, norm[10:11], name = "GM12891")
temp <- matrix(vst.func(as.numeric(conds$GM12892$norm.signal)),
               nrow = nrow(norm))
vst_conds$GM12892 <- bioCond(temp, norm[12:13], name = "GM12892")

# Associate a constant function with the resulting bioConds as their
# mean-variance curve.
vst_conds <- setMeanVarCurve(vst_conds, function(x) rep_len(1, length(x)),
                             occupy.only = TRUE, method = "constant prior")
plotMeanVarCurve(vst_conds, subset = "occupied")

# Make a comparison between GM12891 and GM12892.
res1 <- diffTest(conds$GM12891, conds$GM12892)
res2 <- diffTest(vst_conds$GM12891, vst_conds$GM12892)

# Examine the consistency of analysis results between using ordinary and
# VSTed signal intensities. Here we map p-values together with observed
# directions of signal changes to the standard normal distribution.
z1 <- qnorm(res1$pval / 2)
z1[res1$Mval > 0] <- -z1[res1$Mval > 0]
z2 <- qnorm(res2$pval / 2)
z2[res2$Mval > 0] <- -z2[res2$Mval > 0]
plot(z1, z2, xlab = "Ordinary", ylab = "VSTed")
abline(a = 0, b = 1, lwd = 2, lty = 5, col = "red")
cor(z1, z2)
cor(z1, z2, method = "sp")

# Simultaneously compare GM12890, GM12891 and GM12892 cell lines.
res1 <- aovBioCond(conds)
res2 <- aovBioCond(vst_conds)

# Examine the consistency of analysis results between using ordinary and
# VSTed signal intensities by mapping p-values to the standard normal
# distribution.
z1 <- qnorm(res1$pval, lower.tail = FALSE)
z1[z1 == Inf] <- 39
z2 <- qnorm(res2$pval, lower.tail = FALSE)
z2[z2 == Inf] <- 39
plot(z1, z2, xlab = "Ordinary", ylab = "VSTed")
abline(a = 0, b = 1, lwd = 2, lty = 5, col = "red")
cor(z1, z2)
cor(z1, z2, method = "sp")