Brown, P. J., Driver, B. L., and McConnell, C. (1978) The opportunity spectrum concept and behavioral information in outdoor recreation resource supply inventories : Background and application. Proc. Integr. Renew. Resour. Invent. Workshop,Gen. Tech. Rep. RM-55, USDA For. Serv. : 73-84.
Buist, L. J. and Hoots, T. A. (1982) Recreation opportunity spectrum approach to resource planning. J. For. 80 (2) : 84-86.