Chew, X., and K. W. Khaw. “One-Sided Downward Control Chart for Monitoring the Multivariate Coefficient of Variation With VSSI Strategy”. Journal of Mathematical and Fundamental Sciences, vol. 52, no. 1, Apr. 2020, pp. 112-30, doi:10.5614/j.math.fund.sci.2020.52.1.8.