em.ggb {pickgene}R Documentation

EM calculation for Gamma-Gamma-Bernoulli Model


The function plots contours for the odds that points on microarray show differential expression between two conditions (e.g. Cy3 and Cy5 dye channels on the same microarray).


em.ggb(x, y, theta, start = c(2,1.2,2.7), pprior = 2,
  printit = FALSE, tol = 1e-9, offset = 0 )


x first condition expression levels
y second condition expression levels
theta four parameters a,a0,nu,p
start starting estimates for theta
pprior Beta hyperparameter for prob p of differential expression
printit print iterations if TRUE
tol parameter tolerance for convergence
offset offset added to xx and yy before taking log (can help with negative adjusted values)


Fit Gamma/Gamma/Bernoulli model (equal marginal distributions) The model has spot intensities x ~ Gamma(a,b); y ~ Gamma(a,c). The shape parameters b and c are ~ Gamma(a0,nu). With probability p, b = c; otherwise b != c. All spots are assumed to be independent.


Four parameter vector theta after convergence.


Michael Newton


MA Newton, CM Kendziorski, CS Richmond, FR Blattner and KW Tsui (2000) ``On differential variability of expression ratios: improving statistical inference about gene expression changes from microarray data,'' J Computational Biology 00: 000-000.

See Also



## Not run: 
em.ggb( x, y )
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[Package pickgene version 1.0.0 Index]