For more than half a century, people interested in modeling the movement of people and goods between cities, states or countries have relied on a statistical formula called the gravity law, which measures the “attraction” between two places. Though widely used, the gravity model isn’t very accurate in making predictions. Now CEE Professor Marta González and researchers from Northeastern University and the University of Padua have identified an underlying flaw in the gravity model: The distance between two cities is far less important than the population size in the area surrounding them. The team created a new model that takes human motives into account and in five types of mobility studies the new model’s predictions were far more accurate than the gravity model’s. Read a news release.