Saptiadi Nugroho and  A. Nur Muhamad Afif,  Factors Affecting Employee Performance: A Case Study in Marketing and Trading Directorate, Pertamina Ltd..   journal   = {International Journal of Humanities and Social Sciences}, [online]. World Academy of Science, Engineering and Technology.
    January 2014, vol. 92(8). 2801 - 2804
    [viewed 17 November 2019]. Available from: https://publications.waset.org/pdf/10003777.