Qureshi, M. I., Bashir, N., Zaman, K., Sajjad, N., & Fakhr, S. (2012). Customer Satisfaction Measurement and Analysis Using Six Sigma in Telecom Sector of Pakistan. European Journal of Sustainable Development, 1(1), 53 - 68. https://doi.org/10.14207/ejsd.2012.v1n1p53 - 68