Aliyu, A., B.A Shelleng, and J. Usman. 2018. “FARM LEVEL EFFICIENCY OF RUBBER AS A PERENNIAL CROP USING COBB-DOUGLASS PRODUCTION FRONTIER”. International Journal of Research -GRANTHAALAYAH 6 (7):65-75. https://doi.org/10.29121/granthaalayah.v6.i7.2018.1284.