Yanpanich, V., C. Duangdee, and J. Kunsombat. “Application of Sigma Metrics for the Assessment and Modification of Quality Control in Clinical Chemistry Laboratory of Hospital for Tropical Diseases”. Vajira Medical Journal : Journal of Urban Medicine, vol. 64, no. 6, Dec. 2020, pp. 411-8, doi:10.14456/vmj.2020.40.