Panichkitkosolkul, W. “An Improved Confidence Interval for The Difference Between Standard Deviations of Normal Distributions Using a Ranked Set Sampling”. Journal of Science and Technology, Vol. 12, no. 1, June 2020, pp. 29-40, https://publisher.uthm.edu.my/ojs/index.php/JST/article/view/6106.