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Letters to the Editor |
Department of Biostatistics, and Applied Mathematics, University of Texas, M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Box 447, Houston, TX 77030, Fax 713-563-4242
aE-mail kcoombes{at}mdanderson.org
To the Editor:
I am glad to see that Drs. Fung and Gavin find so much to agree with in my editorial (1). I would, however, like to briefly address their concerns. First, my claim that the Ciphergen software is "extremely conservative" about calling peaks is based on an analysis performed with 24 replicate spectra, which will be published elsewhere (2). We have made the raw spectra available at http://bioinformatics.mdanderson.org/Supplements/Datasets/KuererQC. I urge interested readers to download the data and test the conclusions for themselves. Second, my statement that their baseline correction introduces "substantial bias" should be clarified. Every baseline algorithm I have investigated (including the one we use in our own analyses) introduces substantial bias in peak heights in some portion of the spectrum. In my opinion, the difficulty arises because we do not have a good theoretical understanding of the processes that shape the baseline and must resort to ad hoc algorithms to remove it. One advance in the report by Malyarenko et al. (3) is an explanation of how the physics of the ion detector contributes to the baseline; this is an important first step toward better baseline correction.
References
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