From the Introduction: "The COVID-19 [coronavirus disease 2019] Treatment Guidelines have been developed to inform clinicians how to care for patients with COVID-19. Because clinical information about the optimal management of COVID-19 is evolving quickly, these Guidelines will be updated frequently as published data and other authoritative information become available. The recommendations in these Guidelines are based on scientific evidence and expert opinion. Each recommendation includes two ratings: a letter (A, B, or C) that indicates the strength of the recommendation and a Roman numeral (I, II, or III) that indicates the quality of the evidence that supports the recommendation."
National Institutes of Health: https://www.nih.gov/