Heydari, A., H. Soltani, and M. Mohammadi-Nezhad. 2018. “The Effect of Psychological Skills Training (goal Setting, Positive Selftalk and Imagery) on Self-Confidence of Adolescent Volleyball Players”. Pedagogics, Psychology, Medical-Biological Problems of Physical Training and Sports 22 (4):189-94. https://doi.org/10.15561/18189172.2018.0404.