Hakim, S. N., A. Kalijaga, and S. Indrawati. “SERVICE PERFORMANCE IMPROVEMENT DURING PANDEMIC COVID 19 USING INTEGRATED SERVQUAL AND SIX SIGMA: TELECOMMUNICATION AND INFORMATION INDUSTRY CASE APPLICATION”. Journal of Industrial Engineering and Halal Industries, vol. 1, no. 2, Dec. 2020, pp. 94-101, doi:10.14421/jiehis.2198.