Hierarchical Analysis of Visual COVID-19 Features from Chest Radiographs. - Shruthi Bannur; Ozan Oktay; Melanie Bernhardt; Anton Schwaighofer; Rajesh Jena; Besmira Nushi; Sharan Wadhwani; Aditya V. Nori; Kal Natarajan; Shazad Ashraf; Javier Alvarez-Valle; Daniel C. Castro (CoRR, 2021)