> <i>What is PMMoV normalization?</i><p>> <i>In addition to the pathogens it tests for, WastewaterSCAN measures an extremely common, harmless plant virus that is consumed when people eat. It is called pepper mild mottle virus (or PMMoV). By measuring the concentration of PMMoV genetic markers per dry weight gram of wastewater solids, WastewaterSCAN can account for how much viral material is recovered from each sample and changes to the “fecal strength” of that sample. For example, heavy rain that drains into a wastewater system can dilute the strength of a particular day’s sample.</i><p>OK, that's pretty clever and it sounds useful, so I guess I should turn on that toggle. But then I read further and see this:<p>> <i>Our analysis suggests that both the concentrations of the SARS-CoV-2 genes measured as copies per gram of solid waste and those concentrations normalized by PMMoV are proportional to laboratory confirmed COVID-19 incidence rates in the sewersheds.</i><p>How can both things be proportional? Do they actually mean positively correlated?<p>If raw data is already proportional to lab tests, then it doesn't seem like there's any benefit from normalizing.