1. Department of Biostatistics, University of Iowa, Iowa City, IA, USA
2. Department of Biostatistics, Columbia University, New York, NY, USA
3. Foundation for Interdisciplinary Motor Neuron Medicine, Metamora, MI, USA
4. Palladian Partners, Inc., Silver Spring, MD, USA
5. Statistics Collaborative, Inc., Washington, DC, USA
6. National Institute of Neurological Disorders and Stroke, Bethesda, MD, USA