Comment: Microarrays, Empirical Bayes and the Two-Group Model

Cai, Tommaso

doi:10.1214/07-sts236c

Cited by 1 publication

(1 citation statement)

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“…We tried alternative specifications for the intervals used for estimating the empirical null density and different degrees of freedom for the splines: all yielded very similar results. Moreover, we found that MLE is more sensitive to the choice of the interval [ a , b ] as also observed in [ 24 ]. Next, we applied the proposed constraint estimation approach with the same choices of null intervals.…”

Section: Resultssupporting

confidence: 80%

Analyzing 2D gel images using a two-component empirical bayes model

Seillier-Moiseiwitsch

2011

BMC Bioinformatics

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BackgroundTwo-dimensional polyacrylomide gel electrophoresis (2D gel, 2D PAGE, 2-DE) is a powerful tool for analyzing the proteome of a organism. Differential analysis of 2D gel images aims at finding proteins that change under different conditions, which leads to large-scale hypothesis testing as in microarray data analysis. Two-component empirical Bayes (EB) models have been widely discussed for large-scale hypothesis testing and applied in the context of genomic data. They have not been implemented for the differential analysis of 2D gel data. In the literature, the mixture and null densities of the test statistics are estimated separately. The estimation of the mixture density does not take into account assumptions about the null density. Thus, there is no guarantee that the estimated null component will be no greater than the mixture density as it should be.ResultsWe present an implementation of a two-component EB model for the analysis of 2D gel images. In contrast to the published estimation method, we propose to estimate the mixture and null densities simultaneously using a constrained estimation approach, which relies on an iteratively re-weighted least-squares algorithm. The assumption about the null density is naturally taken into account in the estimation of the mixture density. This strategy is illustrated using a set of 2D gel images from a factorial experiment. The proposed approach is validated using a set of simulated gels.ConclusionsThe two-component EB model is a very useful for large-scale hypothesis testing. In proteomic analysis, the theoretical null density is often not appropriate. We demonstrate how to implement a two-component EB model for analyzing a set of 2D gel images. We show that it is necessary to estimate the mixture density and empirical null component simultaneously. The proposed constrained estimation method always yields valid estimates and more stable results. The proposed estimation approach proposed can be applied to other contexts where large-scale hypothesis testing occurs.

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Section: Resultssupporting

confidence: 80%