The greater variation in volume per address in the U.S. is probably due to the fact that mail volume and income are highly correlated and the fact that the U.S. has a much larger variation in income per household than France.
Mail volume is highest among incomes of over $100,000.
mnli hypothesis: Mail volume is highest among incomes of over $100,000. premise: The greater variation in volume per address in the U.S. is probably due to the fact that mail volume and income are highly correlated and the fact that the U.S. has a much larger variation in income per household than France.