[BioC] About NormExp+offset=50

Saroj K Mohapatra saroj at vt.edu
Mon May 25 20:30:10 CEST 2009

Dear Priscila:

The 'convolution model' is about different distributional properties of 
foreground (signal) and background data on microarray.

 > library(limma)
 > ?normexp.fit

 From the help page of normexp.fit (package: limma)
     The Normal+Exp (normexp) convolution model is a mathematical model
     representing microarray intensity data for the purposes of
     background correction. It was proposed originally as part of the
     RMA algorithm for Affymetrix microarray data. For two-color
     microarry data, the normexp background correction method was
     introduced and compared with other methods by Ritchie et al

     This function uses maximum likelihood estimation to fit the
     normexp model to background-corrected intensities. The model
     assumes that the observed intensities are the sum of background
     and signal components, the background being normal and the signal
     being exponential distributed.

Best wishes,


Priscila Grynberg wrote:
> Dear BioCs,
> Can someone explain to me in an easy way what's a convolutional model? I'm a
> biologist!
> Sincerely,
> Priscila
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