Hi Henrik:

I am looking at SNP 500K data for cell-lines that was released from
GSK.  I followed your example CRMA v2.  with CBS segmentation without
reference samples.  It seems that the scale/dynamic range in the plus
side (amplification) is compressed compared with similar data from
other sources (same CEL file, or same cell-lines).  For example, the
erbbB/Her2 region (chr 17, ~35 mb) in BT474 cell-line, I got relative
copy number ~ 2, which translate to 4 copies.  The same region for
BT474 from Sanger center (their CEL data) has ~ 15 copies, while NCI
cancer genome workbench (same CEL file, not sure what algoruthm) shows
~28 copies.

I realized that many factors could impact copy number calculation,
just want to know your thoughts on this.  Could it duo to using
average as reference? or something specific for your algorithm?

Thanks a lot.

Han Chang
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