Şengül Çelikay, Duygu; Çelikay, Ferdi (2021). "The Effect of COVID-19 on the Tourism Sector in Turkey: An Evaluation with Financial Statement Analysis". Advances in Hospitality, Tourism, and the Services Industry. doi:10.4018/978-1-7998-8231-2.ch004. S2CID237958776.
Şengül Çelikay, Duygu; Çelikay, Ferdi (2021). "The Effect of COVID-19 on the Tourism Sector in Turkey: An Evaluation with Financial Statement Analysis". Advances in Hospitality, Tourism, and the Services Industry. doi:10.4018/978-1-7998-8231-2.ch004. S2CID237958776.