@book{ BA35714040, author = "Porat, Marc Uri and United States. Dept. of Commerce. Office of Telecommunications and National Science Foundation (U.S.)", title = "Definition and measurement", publisher = "U.S. Dept. of Commerce, Office of Telecommunications,For sale by the Supt. of Docs., U.S. Govt. Print. Off.", year = "1977", series = "OT special publication", number = "77-12(1) . The information economy", URL = "https://ci.nii.ac.jp/ncid/BA35714040" }