Maya Ningrum, D. T., Rizkei Kurniawan, and Y. V. Mahyudi. “The Effect of Cooperative Learning and Self Confidence on Service Volleyball At SMPN 4 Negara”. JIPES - JOURNAL OF INDONESIAN PHYSICAL EDUCATION AND SPORT, Vol. 5, no. 1, July 2019, pp. 63-68, http://103.8.12.212:33180/unj/index.php/jipes/article/view/14657.