NBPSeq (version 0.1.8)

nb.glm.test: Fit Negative Binomial Regression Model and Test for a Regression Coefficient

Description

For each row of the input data matrix, nb.glm.test fits a NB log-linear regression model and perform large-sample tests for a one-dimensional regression coefficient.

Usage

nb.glm.test(counts, x, beta0,
    lib.sizes = colSums(counts),
    normalization.method = NULL,
    dispersion.method = "log-linear-rel-mean",
    tests = c("HOA", "LR", "Wald"),
    alternative = "two.sided")

Arguments

counts

an m by n matrix of RNA-Seq read counts with rows corresponding to gene features and columns corresponding to independent biological samples.

x

an n by p design matrix specifiying the treatment structure.

beta0

a p-vector specifying the null hypothesis. Non-NA components specify the parameters to test and their null values. (Currently, only one-dimensional test is implemented, so only one non-NA component is allowed).

lib.sizes

a p-vector of observed library sizes, usually (and by default) estimated by column totals.

normalization.method

a character string specifying the method for estimating the normalization factors, can be NULL or "AH2010". If method=NULL, the normalization factors will have values of 1 (i.e., no normalization is applied);

dispersion.method

a character string specifying the method for estimating the dispersion parameter. Currenlty, the only implemented option is "log-linear-rel-mean", which assumes that log dispersion is a log-linear function of the relative mean.

tests

a character string vector specifying the tests to be performed, can be any subset of "HOA" (higher-order asymptotic test), "LR" (likelihoo ratio test), and "Wald" (Wald test).

alternative

a character string specifying the alternative hypothesis, must be one of "two.sided" (default), "greater" or "less".

Value

• A list containing the following components:
• data
  a list containing the input data matrix with additional summary quantities, output from prepare.nb.data.
• dispersion
  dispersion estimates and models, output from estimate.dispersion.
• test
  test results, output from test.coefficient.

Details

nbp.glm.test provides a simple, one-stop interface to performing a series of core tasks in regression analysis of RNA-Seq data: it calls estimate.norm.factors to estimate normalizaton factors; it calls prepare.nb.data to create a NB data structure; it calls estimate.dispersion to estimete the NB dispersion; and it calls test.coefficient to test the regresssion coefficient.

To keep the interface simple, nbp.glm.test provides limited options for fine tuning models/parameters in each individual step. For more control over individual steps, advanced users can call estimate.norm.factors, prepare.nb.data, estimate.dispersion, and test.coefficient directly, or even substitue one or more of them with their own versions.

Examples

## Load Arabidopsis data
 data(arab);

 ## Use a subset of arab data for demonstration purpose
 counts = arab[1:100,];

 ## Specify treatment structure
 grp.ids = as.factor(c(1, 1, 1, 2, 2, 2));
 x = model.matrix(~grp.ids);

 ## Specify the null hypothesis
 ## The null hypothesis is beta[1]=0 (beta[1] is the log fold change).
 beta0 = c(NA, 0);

 ## Fit NB regression model and perform large sample tests.
 ## The step can take long if the number of genes is large
 fit = nb.glm.test(counts, x, beta0, normalization.method="AH2010");

 ## The result contains the data, the dispersion estimates and the test results
 names(fit);

 ## Show top ten most differentially expressed genes
 subset = order(fit$test.results$HOA$p.values)[1:10];
 cbind(counts[subset,],
       HOA=fit$test.results$HOA$p.values[subset],
       LR=fit$test.results$LR$p.values[subset],
       Wald=fit$test.results$Wald$p.values[subset]
       );