Barida, M., N. . Hidayah, M. Ramli, . A. . Taufiq, and S. Sunaryono. “An Investigation of Item Difficulties in Assertive Communication Based on Yogyakarta Cultural Values”. Pegem Journal of Education and Instruction, vol. 11, no. 4, Oct. 2021, pp. 100-9, doi:10.47750/pegegog.11.04.10.