A. Bilal and M. Aamir, “THREAT OF COVID-19 AND PERCEIVED STRESS: THE MEDIATING ROLE OF CHALLENGE, UNCONTROLLABILITY AND STRESSFULNESS: Threat of COVID-19 And Perceived Stress”, Pak Armed Forces Med J, vol. 71, no. 5, pp. 1571–76, Oct. 2021, doi: 10.51253/pafmj.v71i5.4332.