1. Theory and Practice of the Intensity of Use Method of Mineral Consumption Forecasting;Roberts,1985
2. Is the intensity of copper use still declining in the USA?;Hutchison;Natural Resources Forum,1987
3. Perspectives on intensity of use;Humphreys;Materials and Society,1987
4. The consumption of metals and international trade;Roberts;Materials and Society,1987
5. Personal correspondence, Mr William Black, Copper Development Association, August 1989.