Normexp Model Parameter Estimation Aided by Negative Controls
The mean and log-standard-deviation of the background-normal part of the normexp+exponential convolution model is estimated as the mean and log-standard deviation of intensities from negative control probes. The log-mean of the signal-exponential part is estimated as the log of the difference between signal mean and background mean.
normexp.fit.control(x, status=NULL, negctrl="negative", regular="regular", robust=FALSE)
x |
object of class |
status |
character vector giving probe types. |
negctrl |
character string identifier for negative control probes. |
regular |
character string identifier for regular probes. |
robust |
logical. Should robust estimators be used for the background mean and standard deviation? |
x has to contain raw expression intensities from both regular probes and negative control probes.
The probe type information for an object of EListRaw-class is normally saved in the Status column of its genes component.
However, it will be overriden by the status parameter if it is explicitly provided to this function.
If x is a matrix object, the probe type information has to be provided through the status parameter of this function.
Regular probes have the status regular.
Negative control probes have the status indicated by negctrl, which is negative by default.
This function estimates parameters of the normal+exponential convolution model with the help of negative control probes. The mean and log-standard-deviation of the background-normal part of the normexp+exponential(normexp) convolution model are estimated as the mean and log-standard deviation of intensities from negative control probes respectively. The log-mean of the signal-exponential part is estimated as the log of the difference between signal mean and background mean. The signal mean is simply the mean of intensities from regular probes.
When negative control probes are not available, the normexp.fit.detection.p function can be used to estimate the normexp model parameters which infers the negative control probe intensities from regular probes by taking advantage of their detection p value information.
A matrix containing estimated parameters with rows being arrays and with columns being parameters.
Column names are mu, logsigma and logalpha.
Wei Shi and Gordon Smyth
Shi W, Oshlack A and Smyth GK (2010). Optimizing the noise versus bias trade-off for Illumina Whole Genome Expression BeadChips. Nucleic Acids Research, 38(22):e204. Epub 2010 Oct 6. PMID: 20929874
nec calls this function to get the parameters of the normal+exponential convolution model and then calls normexp.signal to perform the background correction.
normexp.fit.detection.p estimates the parameters in the normal+exponential convolution model using negative control probe intensities inferred from regular probes by using their detection p values information.
normexp.fit estimates normexp parameters using a saddle-point approximation or other mothods.
An overview of background correction functions is given in 04.Background.
## Not run: # read in BeadChip probe profile file and control profile file x <- read.ilmn(files="sample probe profile", ctrlfiles="control probe profile") # estimated normexp parameters normexp.fit.control(x) # normalization using control data y <- neqc(x) ## End(Not run)
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