“…Because of its effectiveness, it has been successfully applied in many applications, e.g., medical diagnosis (Al Rahhal et al, 2019;Shu et al, 2019;Ulloa et al, 2020;Xu et al, 2020), speech processing (Tripathi et al, 2019), and natural language processing (Shi et al, 2018). Although the focal loss has been successfully applied in many real-world problems (Al Rahhal et al, 2019;Chang et al, 2018;Lotfy et al, 2019;Romdhane and Pr, 2020;Shu et al, 2019;Sun et al, 2019;Ulloa et al, 2020;Xu et al, 2020), considerably less attention has *Nontawat and Jayakorn contributed equally. 1 arXiv:2011.09172v2 [stat.ML] 14 Dec 2020 been paid to the theoretical understanding of this loss function.…”