1. Faculty of Medicine and Health Sciences, University of Sherbrooke, Longueuil, Quebec, Canada2Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
2. Douglas Hospital Research Centre, McGill University, Montreal, Quebec, Canada
3. Virginia Tech Transportation Institute, Blacksburg, Virginia5Department of Statistics, Virginia Tech, Blacksburg, Virginia
4. Virginia Tech Transportation Institute, Blacksburg, Virginia
5. Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland
6. Department of Statistics, Virginia Tech, Blacksburg, Virginia