[BioC] asymmetry in up and down regulation

Rafael A. Irizarry ririzarr at jhsph.edu
Mon Aug 11 22:21:21 MEST 2003

remember this only relates to the range of the 12000+ genes. most of the
data is in the orange/yellow area. as described in this list and here:
after that paper was published, some have found 2 other
genes that appear to be spike-ins that affymetrix forgot to report. if you
redefine those as true positives the bias you describe goes away and the
range goes down significantly for both.
because pm-only dchip attenuates signal more than rma, the
bias appears bigger for RMA if you include the new found spikeins as false
positives. becuase of MAS 5's huge variance at the low end the range is
not affected by considering these two genes as false positives.

plots similar to Figure 5 in the NAR paper can be found in the affycomp  
web page stated above (see Figure 6a and 6b). 

hope this helps,
On Mon, 11 Aug 2003, Chris Paulse wrote:

> Figure 5 in the recent Nucleic Acids Research 2003, Vol. 31, No. 4 e15
> (http://nar.oupjournals.org/cgi/content/full/31/4/e15/GNG015F5) shows an 
> interesting asymmetry in the distribution of fold changes for non-spiked in 
> genes.  Can anyone comment on the reason for this?  Here, dChip has the 
> least amount of bias.
> Thanks,
> Chris
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