Stefan Hunger, J. Thomas Sims and Donald L. Sparks
Journal of Environmental Quality 37 ( 4 ): 1617 - 1625 , 2008
Jennifer M. Seiter, Kristin E. Staats-Borda, Matthew Ginder-Vogel and Donald L. Sparks
Journal of Environmental Quality 37 ( 2 ): 477 - 485 , 2008