| Caution about correlation | Currently, there are many gene co-expression databases available that provide correlation coefficients for the relative expression levels of different genes, generally from multiple experiments with different experimental conditions (see e.g., [18]). |
| Caution about correlation | As far as we are aware, none of the database providers explicitly address whether absolute levels of gene expression were constant across experimental conditions . |
| Correlations between relative abundances tell us absolutely nothing | We stress in the absence of any other information or assumptions to highlight the common assumption of constant absolute abundance of total mRNA across all experimental conditions . |
| Proportionality is meaningful for relative data | If relative abundances x and y are proportional across experimental conditions 1', their absolute abundances must be in |