SungJin Cho, "An Empirical Model of Mainframe Computer Investment", Journal of Applied Econometrics, Vol. 26, No. 1, 2011, pp. 122-150. The data used in this paper are very confidential data and the property of one of the largest telecommunications companies in the world. The company handles over 60 percent of all telephone services in its particular market. It also offers several other telecommunication services,including cellular PCS (Personal Communications Service),internet, cable, and satellite communication services. The computer systems in this company can be divided into two categories according to their use: (i) research, and (ii) management and/or delivering services. Further details about the data and the estimation methods may be found in the supplementary file cho-supplement.pdf. SungJin Cho sungcho [AT] snu.ac.kr