A reduced set of potential predictor variables was selected a priori, including patient demographic information, common clinical investigations, and parameters consistently identified as clinically important in covid-19 cohorts following the methods described by Wynants and colleagues (appendix 2).5 Candidate predictor variables were selected based on three common criteria15: patient and clinical variables known to influence outcome in pneumonia and flulike illness; clinical biomarkers previously identified within the literature as potential predictors in patients with covid-19; values available for at least two thirds of patients within the derivation cohort.