1. Department of Environmental Quality of the State of Michigan, 2003a, Production of oil and gas wells database, 1981–1990 production: Lansing, Michigan, Office of Geological Survey [Michigan], downloaded November 3, 2005 from URL http://www.michigan.gov/deq
2. Department of Environmental Quality of the State of Michigan, 2003b, Production of oil and gas wells database, 1991–2000 production: Lansing, Michigan, Office of Geological Survey [Michigan], downloaded November 3, 2005 from URL http://www.michigan.gov/deq
3. Department of Environmental Quality of the State of Michigan, 2005a, Production of oil and gas wells database, 2001–2003 production: Lansing, Michigan, Office of Geological Survey [Michigan], downloaded November 3, 2005 from URL http://www.michigan.gov/deq
4. Department of Environmental Quality of the State of Michigan, 2005b, Production of oil and gas wells database, 2004–2005 production: Lansing, Michigan, Office of Geological Survey [Michigan], downloaded November 3, 2005 from URL http://www.michigan.gov/deq
5. Efron, B., and Gong, G., 1983, A leisurely look at the bootstrap, the jacknife, and cross-validation: American Statistician, v. 37, no. 1, p. 36–48.