Exon Array average gene expression index as a function of transcript (mRNA) length. There is a highly significant positive correlation of expression and length (R = 0.18, p < 10-20). This effect is most likely an artefact of the edge bias illustrated in Figure 7; short transcripts have a lower overall efficiency of first strand synthesis and appear to be expressed at lower levels. The effect is not observed in the 3' amplified U133 (R = 0.05) and Illumina (R = -0.03) results.
Bemmo et al. BMC Genomics 2008 9:529 doi:10.1186/1471-2164-9-529