Bioinformatics Vol. 19 no. 11 2003
Pages 1348-1359
© 2003 Oxford University Press
Noise sampling method: an ANOVA approach allowing robust selection of differentially regulated genes measured by DNA microarrays
1 Department of Computer Science, Wayne State University,
431 State Hall, Detroit, MI, 48202, USA
2 BioDiscovery Inc., 4640 Admiralty Way, Suite 710, Marena del
Rey, CA 90292, USA
3 Karmanos Cancer Institute, Wayne State University
Detroit, MI, 48201, USA
Received on December 15, 2002
; revised on January 22, 2003
; accepted on January 29, 2003
Motivation: A crucial step in microarray data analysis is the selection of subsets of interesting genes from the initial set of genes. In many cases, especially when comparing a specific condition to a reference, the genes of interest are those which are differentially expressed. Two common methods for gene selection are: (a) selection by fold difference (at least n fold variation) and (b) selection by altered ratio (at least n standard deviations away from the mean ratio).
Results: The novel method proposed here is based on ANOVA and uses replicate spots to estimate an empirical distribution of the noise. The measured intensity range is divided in a number of intervals. A noise distribution is constructed for each such interval. Bootstrapping is used to map the desired confidence levels from the noise distribution corresponding to a given interval to the measured log ratios in that interval. If the method is applied on individual arrays having replicate spots, the method can calculate an overall width of the noise distribution which can be used as an indicator of the array quality. We compared this method with the fold change and unusual ratio method. We also discuss the relationship with an ANOVA model proposed by Churchill et al.
In silico experiments were performed while controlling the degree of regulation as well as the amount of noise. Such experiments show the performance of the classical methods can be very unsatisfactory. We also compared the results of the 2-fold method with the results of the noise sampling method using pre and post immortalization cell lines derived from the MDAH041 fibroblasts hybridized on Affymetrix GeneChip arrays. The 2-fold method reported 198 genes as upregulated and 493 genes as downregulated. The noise sampling method reported 98 gene upregulated and 240 genes downregulated at the 99.99% confidence level. The methods agreed on 221 genes downregulated and 66 genes upregulated. Fourteen genes from the subset of genes reported by both methods were all confirmed by Q-RT-PCR. Alternative assays on various subsets of genes on which the two methods disagreed suggested that the noise sampling method is likely to provide fewer false positives.
Contact: sod{at}cs.wayne.edu
* To whom correspondence should be addressed.
The authors wish it to be known that, in their
opinion, the first two authors should be regarded as joint First
Authors.
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