Read counts of a gene in RNA-seq studies, are associated to both gene length and expression level. Some papers (like: http://genomebiology.com/2013/14/9/R95) refer to voomlimma and cuffdiff methods as gene-specific normalization approaches. Does this mean that they take into account the gene length as a factor of normalization or there are some more factors in gene-specific normalization approaches?
Cuffdiff explicitly incorporates gene length, since it uses FPKMs/RPKMs. voom() from the limma packages does't use the gene size at all (any argument that I can come up with that makes the voom method more/less gene-specific is pretty weak). There are also other normalization methods that can take utilize gene-length and gene GC content in normalizations, such as CQN, though I really haven't seen a huge benefit from that in most datasets that I've used (your mileage may vary).