An Econometric Study of the Demand for First and Second Class Inland Letter Services
估计了1976-88年英国一等和二等国内信件的动态季度模型，发现一等信件需求受总支出影响大，而二等信件较弱，两者均对自身及电话价格等有反应。
A dynamic quarterly model for both first and second class U.K. inland letter traffic is estimated over the period 1976-88. The demand for first class letters is strongly influenced by aggregate expenditure, but for second class letters this linkage is much weaker. Both letter streams respond to changes in the price of first and second class letters, the price of telephone services, and other prices as measured by an aggregate price index. Copyright 1990 by MIT Press.