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    Archive for January 27th, 2010

    R script to filter probesets with log-expression values below the lowest spike-in

    27th January 2010

    Sometimes there is a need to remove all the probesets, which have expression values below the minimal spike-in intensity on the Affymetrix microarray. The reasoning behind this procedure is simple: minimal-expression spike-ins represent the bottom margin of microarray sensitivity, and anything below that margin cannot be reliably quantified – which also means that both fold-change and p-value of expression variance will be unreliable for these probesets.

    Here’s a simple R script to do just that. It is abundantly commented, and also contains an optional (commented out) fragment which allows the removal of more low-variance, low-intensity probesets.

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