Research Proximity and Productivity: Long-Term Evidence from Agriculture
利用19世纪末美国赠地学院农业实验站的设立，研究发现靠近研究站能提升土地生产率约20年，之后效应减弱，表明空间摩擦降低了公共研究的回报率，但推广项目、汽车和电话等缓解了这种摩擦。
We use the late nineteenth-century establishment of agricultural experiment stations at preexisting land-grant colleges across the United States to estimate the importance of proximity to research for productivity growth. Our analysis reveals that proximity to newly opened permanent stations affected land productivity for about 20 years and then subsequently declined until becoming largely absent today. We conclude that spatial frictions substantially reduced the rate of return to public research spending in the late nineteenth and early twentieth centuries, but such frictions significantly diminished as extension programs, automobiles, and telephones made it easier for discoveries to reach farther farms.