BASiCS_MCMC {BASiCS} | R Documentation

## BASiCS MCMC sampler

### Description

MCMC sampler to perform Bayesian inference for single-cell mRNA sequencing datasets using the model described in Vallejos et al (2015).

### Usage

    BASiCS_MCMC(Data, N, Thin, Burn, Regression, WithSpikes = TRUE, ...)

### Arguments

`Data` | A `SingleCellExperiment` object. If `WithSpikes = TRUE`, this MUST be formatted to include the spike-ins and/or batch information (see vignette).
`N` | Total number of iterations for the MCMC sampler. Use `N>=max(4,Thin)`, `N` being a multiple of `Thin`.
`Thin` | Thining period for the MCMC sampler. Use `Thin>=2`.
`Burn` | Burn-in period for the MCMC sampler. Use `Burn>=1`, `Burn<N`, `Burn` being a multiple of `Thin`.
`Regression` | If `Regression = TRUE`, BASiCS exploits a joint prior formulation for mean and over-dispersion parameters to estimate a measure of residual over-dispersion is not confounded by mean expression. Recommended setting is `Regression = TRUE`.
`WithSpikes` | If `WithSpikes = TRUE`, BASiCS will use reads from added spike-ins to estimate technical variability. If `WithSpikess = FALSE`, BASiCS depends on replicated experiments (batches) to estimate technical variability. In this case, please supply the BatchInfo vector in `colData(Data)`. Default: `WithSpikes = TRUE`.
`...` | Optional parameters. `PriorDelta` Specifies the prior used for `delta`. Possible values are 'gamma' (Gamma(`a.theta`,`b.theta`) prior) and 'log-normal' (log-Normal(`0`,`s2.delta`) prior) . . Default value: `PriorDelta = 'log-normal'`. `PriorParam` List of 7 elements, containing the hyper-parameter values required for the adopted prior (see Vallejos et al, 2015, 2016). All elements must be positive real numbers. `s2.mu` Scale hyper-parameter for the log-Normal(`0`,`s2.mu`) prior that is shared by all gene-specific expression rate parameters μ_i. Default: `s2.mu = 0.5`. `s2.delta` Only used when ‘PriorDelta == ’log-normal''. Scale hyper-parameter for the log-Normal(`0`,`s2.delta`) prior that is shared by all gene-specific over-dispersion parameters δ_i. Default: `s2.delta = 0.5`. `a.delta` Only used when ‘PriorDelta == ’gamma''. Shape hyper-parameter for the Gamma(`a.delta`,`b.delta`) prior that is shared by all gene-specific biological over-dispersion parameters δ_i. Default: `a.delta = 1`. `b.delta` Only used when ‘PriorDelta == ’gamma''. Rate hyper-parameter for the Gamma(`a.delta`,`b.delta`) prior that is shared by all gene-specific biological over-dispersion hyper-parameters δ_i. Default: `b.delta = 1`. `p.phi` Dirichlet hyper-parameter for the joint of all (scaled by `n`) cell-specific mRNA content normalising constants φ_j / n. Default: `p.phi` `= rep(1, n)`. `a.s` Shape hyper-parameter for the Gamma(`a.s`,`b.s`) prior that is shared by all cell-specific capture efficiency normalising constants s_j. Default: `a.s = 1`. `b.s` Rate hyper-parameter for the Gamma(`a.s`, `b.s`) prior that is shared by all cell-specific capture efficiency normalising constants s_j. Default: `b.s = 1`. `a.theta` Shape hyper-parameter for the Gamma(`a.theta`,`b.theta`) prior for technical noise parameter θ. Default: `a.theta = 1`. `b.theta` Rate hyper-parameter for the Gamma(`a.theta`,`b.theta`) prior for technical noise parameter θ. Default: `b.theta = 1`. `eta` Only used when `Regression = TRUE`. `eta` specifies the degress of freedom for the residual term. Default: `eta = 5`. . `k` Only used when `Regression = TRUE`. `k` specifies the number of regression Gaussian Radial Basis Functions (GRBF) used within the correlated prior adopted for gene-specific over-dispersion and mean expression paramters. Default: `k = 12`. `Var` Only used when `Regression = TRUE`. `Var` specifies the GRBF scaling parameter. Default: `Var = 1.2`. `AR` Optimal acceptance rate for adaptive Metropolis Hastings updates. It must be a positive number between 0 and 1. Default (and recommended): `AR = 0.44` . `StopAdapt` Iteration at which adaptive proposals are not longer adapted. Use `StopAdapt>=1`. Default: `StopAdapt = Burn`. `StoreChains` If `StoreChains = TRUE`, the generated `BASiCS_Chain` object is stored as a '.Rds' file (`RunName` argument used to index the file name). Default: `StoreChains = FALSE`. `StoreAdapt` If `StoreAdapt = TRUE`, trajectory of adaptive proposal variances (in log-scale) for all parameters is stored as a list in a '.Rds' file (`RunName` argument used to index file name). Default: `StoreAdapt = FALSE`. `StoreDir` Directory where output files are stored. Only required if `StoreChains = TRUE` and/or `StoreAdapt = TRUE`). Default: `StoreDir = getwd()`. `RunName` String used to index '.Rds' files storing chains and/or adaptive proposal variances. `PrintProgress` If `PrintProgress = FALSE`, console-based progress report is suppressed. `Start` Starting values for the MCMC sampler. We do not advise to use this argument. Default options have been tuned to facilitate convergence. If changed, it must be a list containing the following elements: `mu0`, `delta0`, `phi0`, `s0`, `nu0`, `theta0`, `ls.mu0`, `ls.delta0`, `ls.phi0`, `ls.nu0` and `ls.theta0`

### Value

An object of class `BASiCS_Chain`.

### Author(s)

Catalina A. Vallejos cnvallej@uc.cl

Nils Eling eling@ebi.ac.uk

### References

Vallejos, Marioni and Richardson (2015). PLoS Computational Biology.

Vallejos, Richardson and Marioni (2016). Genome Biology.

Eling et al (2018). Cell Systems

### Examples

    # Built-in simulated dataset
    set.seed(1)
    Data <- makeExampleBASiCS_Data()
    # To analyse real data, please refer to the instructions in:
    # https://github.com/catavallejos/BASiCS/wiki/2.-Input-preparation

    # Only a short run of the MCMC algorithm for illustration purposes
    # Longer runs migth be required to reach convergence
    Chain <- BASiCS_MCMC(Data, N = 50, Thin = 2, Burn = 10, Regression = FALSE,
                         PrintProgress = FALSE, WithSpikes = TRUE)

    # To run the regression version of BASiCS, use:
    Chain <- BASiCS_MCMC(Data, N = 50, Thin = 2, Burn = 10, Regression = TRUE,
                         PrintProgress = FALSE, WithSpikes = TRUE)

    # To run the non-spike version BASiCS requires the data to contain at least
    # 2 batches:
    set.seed(2)
    Data <- makeExampleBASiCS_Data(WithBatch = TRUE)
    Chain <- BASiCS_MCMC(Data, N = 50, Thin = 2, Burn = 10, Regression = TRUE,
                         PrintProgress = FALSE, WithSpikes = FALSE)

    # For illustration purposes we load a built-in 'BASiCS_Chain' object
    # (obtained using the 'BASiCS_MCMC' function)
    data(ChainSC)

    # `displayChainBASiCS` can be used to extract information from this output.
    # For example:
    head(displayChainBASiCS(ChainSC, Param = 'mu'))

    # Traceplot (examples only)
    plot(ChainSC, Param = 'mu', Gene = 1)
    plot(ChainSC, Param = 'phi', Cell = 1)
    plot(ChainSC, Param = 'theta', Batch = 1)

    # Calculating posterior medians and 95% HPD intervals
    ChainSummary <- Summary(ChainSC)

    # `displaySummaryBASiCS` can be used to extract information from this output
    # For example:
    head(displaySummaryBASiCS(ChainSummary, Param = 'mu'))

    # Graphical display of posterior medians and 95% HPD intervals
    # For example:
    plot(ChainSummary, Param = 'mu', main = 'All genes')
    plot(ChainSummary, Param = 'mu', Genes = 1:10, main = 'First 10 genes')
    plot(ChainSummary, Param = 'phi', main = 'All cells')
    plot(ChainSummary, Param = 'phi', Cells = 1:5, main = 'First 5 cells')
    plot(ChainSummary, Param = 'theta')

    # To constrast posterior medians of cell-specific parameters
    # For example:
    par(mfrow = c(1,2))
    plot(ChainSummary, Param = 'phi', Param2 = 's', SmoothPlot = FALSE)
    # Recommended for large numbers of cells
    plot(ChainSummary, Param = 'phi', Param2 = 's', SmoothPlot = TRUE)

    # To constrast posterior medians of gene-specific parameters
    par(mfrow = c(1,2))
    plot(ChainSummary, Param = 'mu', Param2 = 'delta', log = 'x',
         SmoothPlot = FALSE)
    # Recommended
    plot(ChainSummary, Param = 'mu', Param2 = 'delta', log = 'x',
         SmoothPlot = TRUE)

    # To obtain denoised rates / counts, see:
    # help(BASiCS_DenoisedRates)
    # and
    # help(BASiCS_DenoisedCounts)

    # For examples of differential analyses between 2 populations of cells see:
    # help(BASiCS_TestDE)

[Package BASiCS version 1.8.1 Index]