Mohamed Arip, M. A. S. “Analysis of Validity and Reliability of Survey Self-Assessment Scale-PEER (SPKK-RS) (1 - 22)”. Jurnal Pendidikan Bitara UPSI, vol. 4, no. 1, May 2019, pp. 1-22, https://ojs.upsi.edu.my/index.php/JPB/article/view/2396.