Abstract
(1) Background: Gene-expression data usually contain missing values (MVs). Numerous methods focused on how to estimate MVs have been proposed in the past few years. Recent studies show that those imputation algorithms made little difference in classification. Thus, some scholars believe that how to select the informative genes for downstream classification is more important than how to impute MVs. However, most feature-selection (FS) algorithms need beforehand imputation, and the impact of beforehand MV imputation on downstream FS performance is seldom considered. (2) Method: A modified chi-square test-based FS is introduced for gene-expression data. To deal with the challenge of a small sample size of gene-expression data, a heuristic method called recursive element aggregation is proposed in this study. Our approach can directly handle incomplete data without any imputation methods or missing-data assumptions. The most informative genes can be selected through a threshold. After that, the best-first search strategy is utilized to find optimal feature subsets for classification. (3) Results: We compare our method with several FS algorithms. Evaluation is performed on twelve original incomplete cancer gene-expression datasets. We demonstrate that MV imputation on an incomplete dataset impacts subsequent FS in terms of classification tasks. Through directly conducting FS on incomplete data, our method can avoid potential disturbances on subsequent FS procedures caused by MV imputation. An experiment on small, round blue cell tumor (SRBCT) dataset showed that our method found additional genes besides many common genes with the two compared existing methods.
Highlights
As an important technology in the field of bioinformatics, microarray technology is prominent do to its ability to potentially simultaneously measure thousands of gene-expression levels [1,2]
Gene-expression data are important data obtained from microarray experiments
For real data, missing values (MVs) imputation has minor impact on downstream classification tasks, but MV imputation is based on the MAR assumption; the impact of MV imputation on subsequent FS is seldom considered
Summary
As an important technology in the field of bioinformatics, microarray technology is prominent do to its ability to potentially simultaneously measure thousands of gene-expression levels [1,2]. Gene-expression data obtained from microarray experiments are usually confronted with high-dimension and missing-data problems [3,4]. This characteristic generates two problems for downstream gene-expression data analysis (e.g., classification). MVs present a challenge to traditional analysis models that require a complete data matrix [5,6]. Another problem is the high computational complexity caused by data’s high dimensionality [7,8]
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