text: The general goal of the technique is similar to the DNA microarray.  However, SAGE sampling is based on sequencing mRNA output, not on hybridization of mRNA output to probes, so transcription levels are measured more quantitatively than by microarray.  In addition, the mRNA sequences do not need to be known a priori, so genes or gene variants which are not known can be discovered.  Microarray experiments are much cheaper to perform, so large-scale studies do not typically use SAGE.  Quantifying gene expressions is more exact in SAGE because it involves directly counting the number of transcripts whereas spot intensities in microarrays fall in non-discrete gradients and are prone to background noise.