1 Department of Biostatistics, Yale School of Public Health, New Haven, CT, USA.
2 Department of Biostatistics, Epidemiology and Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
3 Palliative and Advanced Illness Research (PAIR) Center and Pulmonary and Critical Care Division, Department of Medicine, Perelman School of Medicine, University of Pennsylvania, PA, USA.