In molecular bioscience, measurements of relative abundance are, well… abundant. However, appreciation of the need to analyse and interpret these data differently to measurements of absolute abundance is scarce.
Correlation is one of the workhorses of quantitative bioscience, but people do not always realise that it should not be used for data that carry only relative information.
This short video uses cookbooks, thrillers, and a bit of 3D geometry to explain why correlation is not OK for proportions, percentages and parts-per-million.
And, just in case you are wondering whether you are working with relative abundance data, ask yourself “Would doubling the amount of starting material double my measurements?”
If the answer is no, then you are working with relative information and should steer clear of correlation!