13 The smaller variation in U.S. postal densities is due to differences in the quality of delivery service which dampen the impact of low population density on many routes.
US postal density doesn't change at all.
mnli hypothesis: US postal density doesn't change at all. premise: 13 The smaller variation in U.S. postal densities is due to differences in the quality of delivery service which dampen the impact of low population density on many routes.