Ahmad Ridha Syiah Kuala University   Kopelma Darussalam, Syiah Kuala Banda Aceh, Aceh 23111 Indonesia   achmad.ridha@gmail.com   http://s3ie.unsyiah.ac.id/profil-prodi-die-feb-unsyiah           JEL Areas: A1 : General Economics: General D4 : Market Structure and Pricing: General