It's entirely possible to analyze literal shit to estimate drug use patterns of whole cities. In fact, as I've reported before, wastewater drug analysis—sampling raw sewage for traces of illicit substances—is common practice in many parts of the world, including Europe, Australia, China, and parts of the United States.
But one of the biggest blind spots in this research is accurately estimating real time population size, which changes over the course of the year. (In statistics, this is known as censoring.) After all, the citizenry of a city like London can wildly vary due to factors like tourism and commuting—how do you know whose cocaine-soaked urine comes from whom?
A new study from the Norwegian Institute for Water Research suggests using mobile phone trace data to accurately peg population drug use—in other words, tracking cell phone pings and correlating them with how much MDMA is in the sewage.
Read more here