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<body bgcolor = "#FFFFCC"><basefont face = "Arial"> |
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<h1>Variance Filter</h1><h2>Parameter Information</h2> |
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The variance filter allows the removal of genes with low variation of expression over the |
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loaded samples. This filter is basically used to remove ‘flat genes’ that don’t vary much |
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in expression over the conditions of the experiment. The variance filter has three possible |
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criteria for specifying which genes to keep. The Enable Variance Filter check box turns the |
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filter on and off. Be sure to observe the History Node log to see the number of genes |
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retained after using the filter. Note that the variance filter is performed after other |
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filters such as Percent Cutoff Filter is imposed. This convention insures that the genes |
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that are tested for variance also contain some minimum level of ‘good’ (not missing) data. |
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<h2>Percentage of Highest SD Genes</h2> |
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The <i>Percentage of Highest SD Genes</i> option ranks the genes based on standard deviation and |
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then the genes that are kept are some percentage of this ranked list. For and example, |
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if we have 1000 genes and the percentage was set to 20%, then the result would be a |
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final list of the 200 most variable genes. |
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<h2>Number of Desired High SD Genes</h2> |
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The <i>Number of Desired High SD Genes</i> option also ranks the genes based on SD and |
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then the number of genes specified are selected from this SD ordered list such that |
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the highest SD genes are selected. |
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<h2>SD Cutoff Value</h2> |
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The <i>SD Cutoff Value</i> option uses an actual SD value such that all genes having |
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an SD greater than this value are selected. |
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