combineTests {csaw} | R Documentation

## Combine statistics across multiple tests

### Description

Combines p-values across clustered tests using Simes' method to control the cluster-level FDR.

### Usage

    combineTests(
      ids,
      tab,
      weights = NULL,
      pval.col = NULL,
      fc.col = NULL,
      fc.threshold = 0.05
    )

### Arguments

`ids` | An integer vector or factor containing the cluster ID for each test.
`tab` | A data.frame of results with `PValue` and at least one `logFC` field for each test.
`weights` | A numeric vector of weights for each test. Defaults to 1 for all tests.
`pval.col` | An integer scalar or string specifying the column of `tab` containing the p-values. Defaults to `"PValue"`.
`fc.col` | An integer or character vector specifying the columns of `tab` containing the log-fold changes. Defaults to all columns in `tab` starting with `"logFC"`.
`fc.threshold` | A numeric scalar specifying the FDR threshold to use within each cluster for counting tests changing in each direction, see `?"cluster-direction"` for more details.

### Details

All tests with the same value of `ids` are used to define a single cluster. This function applies Simes' procedure to the per-test p-values to compute the combined p-value for each cluster, which represents evidence against the global null hypothesis, i.e., all individual nulls are true in each cluster. The BH method is then applied to control the FDR across all clusters.

Rejection of the global null is more relevant than the significance of each individual test when multiple tests in a cluster represent parts of the same underlying event, e.g., differentially bound genomic regions consisting of clusters of windows. Control of the FDR across tests may not equate to control of the FDR across clusters; we ensure the latter by explicitly computing cluster-level p-values for use in the BH method.

We use Simes' method as it is relatively relaxed and rejects the global null upon observing any change in the cluster. More stringent methods are available in functions like `minimalTests` and `getBestTest`.

The importance of each test within a cluster can be adjusted by supplying different relative `weights` values. This may be useful for downweighting low-confidence tests, e.g., those in repeat regions. In Simes' procedure, weights are interpreted as relative frequencies of the tests in each cluster. Note that these weights have no effect between clusters.

To obtain `ids`, a simple clustering approach for genomic windows is implemented in `mergeWindows`. However, anything can be used so long as it is independent of the p-values and does not compromise type I error control, e.g., promoters, gene bodies, independently called peaks. Any tests with `NA` values for `ids` will be ignored.

### Value

A DataFrame with one row per cluster and various fields:

- An integer field `num.tests`, specifying the total number of tests in each cluster.

- Two integer fields `num.up.*` and `num.down.*` for each log-FC column in `tab`, containing the number of tests with log-FCs significantly greater or less than 0, respectively. See `?"cluster-direction"` for more details.

- A numeric field containing the cluster-level p-value. If `pval.col=NULL`, this column is named `PValue`, otherwise its name is set to `colnames(tab[,pval.col])`.

- A numeric field `FDR`, containing the BH-adjusted cluster-level p-value.

- A character field `direction` (if `fc.col` is of length 1), specifying the dominant direction of change for tests in each cluster. See `?"cluster-direction"` for more details.

- One integer field `rep.test` containing the row index (for `tab`) of a representative test for each cluster. See `?"cluster-direction"` for more details.

- One numeric field `rep.*` for each log-FC column in `tab`, containing a representative log-fold change for the differential tests in the cluster. See `?"cluster-direction"` for more details.

Each row is named according to the ID of the corresponding cluster.

### Author(s)

Aaron Lun

### References

Simes RJ (1986). An improved Bonferroni procedure for multiple tests of significance. Biometrika 73, 751-754.

Benjamini Y and Hochberg Y (1995). Controlling the false discovery rate: a practical and powerful approach to multiple testing. J. R. Stat. Soc. Series B 57, 289-300.

Benjamini Y and Hochberg Y (1997). Multiple hypotheses testing with weights. Scand. J. Stat. 24, 407-418.

Lun ATL and Smyth GK (2014). De novo detection of differentially bound regions for ChIP-seq data using peaks and windows: controlling error rates correctly. Nucleic Acids Res. 42, e95

### See Also

`mergeWindows`, for one method of generating `ids`.

`glmQLFTest`, for one method of generating `tab`.

### Examples

    ids <- round(runif(100, 1, 10))
    tab <- data.frame(logFC=rnorm(100), logCPM=rnorm(100), PValue=rbeta(100, 1, 2))
    combined <- combineTests(ids, tab)
    head(combined)

    # With window weighting.
    w <- round(runif(100, 1, 5))
    combined <- combineTests(ids, tab, weights=w)
    head(combined)

    # With multiple log-FCs.
    tab$logFC.whee <- rnorm(100, 5)
    combined <- combineTests(ids, tab)
    head(combined)

    # Manual specification of column IDs.
    combined <- combineTests(ids, tab, fc.col=c(1,4), pval.col=3)
    head(combined)

    combined <- combineTests(ids, tab, fc.col="logFC.whee", pval.col="PValue")
    head(combined)

[Package csaw version 1.21.4 Index]