2D visualization of integrity categories. The figure shows a projection of the categories onto the two-dimensional space spanned by the first two features of the selected combination. These are total RNA ratio and 28S peak height. The experiments are clearly grouped along a curve from the left bottom corner up to the top and then to the right top corner. The variance in location of the experiments increases with larger categorical value. Categories 1 and 2 have almost no variance in this feature space. The grey border in the domain is given by the abnormality detectors for this two variables, i.e., for a data point outside the white area no RIN is computed.