By searching through household waste, which is dumped in bins on street corners in the city, she was able to detect clear differences between districts. There was ample evidence of drug abuse in lower-income quarters, for instance. And in one area, she and her team were surprised to find an unusual amount of paper in the waste bags they examined. It turned out that the local population had changed in recent years and now represented a group of unfortunate middle-class individuals, who were more likely to be readers of newspapers than lower-class inhabitants.