Mulyaningsih, May, et al. “Analysis of Covid-19 Impact on Stock’s Abnormal Return in Sub Cigarette Sector Companies Listed on BEI”. Journal of Social Transformation and Regional Development, vol. 3, no. 1, June 2021, pp. 70-84, https://penerbit.uthm.edu.my/ojs/index.php/jstard/article/view/7604.