1. Department of Public Administration, North Carolina Central University, 215 Whiting CJ Building, Durham, North Carolina 27707, United States
2. Nicholas School of the Environment, Duke University, Box 90328, Durham, North Carolina 27708, United States
3. North Carolina Geological Survey, 1620 Mail Service Center, Raleigh, North Carolina 27699, United States
4. Department of Statistical Science, Duke University, Box 90251, Durham, North Carolina 27708, United States