spatialCorrection {RPPASPACE} | R Documentation |
Spatial Correction
Description
This function estimates a smoothed surface from positive control spots on
an RPPA slide. The surface is used to perform spatial corrections (i.e.,
because of uneven hybridization) on the array.
It is used before RPPAFit
, one slide at a time.
Usage
spatialAdjustmentFromParams(rppa,
spatialparams)
spatialAdjustment(rppa,
cutoff=0.8,
k=100,
gamma=0.1,
plotSurface=FALSE)
spatialCorrection(rppa,
measure=c("Net.Value", "Raw.Value"),
cutoff=0.8,
k=100,
gamma=0.1,
plotSurface=FALSE)
Arguments
rppa |
object of class |
spatialparams |
object of class |
measure |
character string specifying fit measure to smooth |
cutoff |
numeric scalar used to identify the background cutoff with value in range [0..1] |
k |
numeric scalar used as smoothing model argument. |
gamma |
numeric scalar used as model parameter with value in range [0..2] |
plotSurface |
logical scalar. If |
Details
The observed spot intensities are assumed to be a combination of true signal, background noise, and hybridization effects according to the following model:
Y_rc = Y * H_rc + B_rc
where Y_rc
is the observed intensity, Y
is the true signal,
H_rc
is the effect of hybridization, and B_rc
is the
background noise. The subscripts "r" and "c" refer to the physical row
and column of the spot on the array. Background noise is estimated
locally by the array software. The hybridization effect is estimated
fitting a generalized additive model (GAM) to positive control
spots printed uniformly across the array.
The estimated surface is used to scale the intensities on the array. Each intensity is adjusted by the amount that is needed to make the positive control surface flat at the value of the median of the surface. This is done by dividing each spot by the estimated surface value and then multiplying by the median of the surface.
Positive control spots that are expressed below the cutoff for the noise region are excluded from the computation of the surface.
Sometimes, positive control spots are printed in a dilution series to avoid saturation problems with these spots. When this happens, the observed intensities are adjusted by the positive control surface that has the most similar expression level.
The cutoff
argument passed to quantile
is percentile
of the background estimates used to define the noise region of slide.
The k
argument passed to s
sets upper limit on
degrees of freedom associated with smoothing.
The gamma
argument passed to gam
provides a constant
multiplier used to inflate model degrees of freedom in the
GCV or UBRE/AIC score.
Value
Returns modified rppa
with an additional measurement column
named after the measure
with an Adj.
prefix. For example,
if the measure was Net.Value
, the name of the adjusted column
would be Adj.Net.Value
.
Author(s)
P. Roebuck paul_roebuck@comcast.net, E. Shannon Neeley sneeley@stat.byu.edu, James M. Melott jmmelott@mdanderson.org
References
Neeley ES, Baggerly KA, Kornblau SM.
Surface Adjustment of Reverse Phase Protein Arrays Using Positive
Control Spots
Cancer Informatics (2012) 11: 77-86.
https://pubmed.ncbi.nlm.nih.gov/22550399/
See Also
RPPASpatialParams
,
quantile
,
gam
,
s
,
choose.k