Edeme, R. K. . ., C. N. . . Nkalu, B. . Azu, and S. C. . Nwachukwu. “Alternative Specification and Estimation of Tax Revenue-Gross Domestic Product Relationship”. Asian Journal of Economic Modelling, vol. 4, no. 3, Apr. 2016, pp. 134-41, doi:10.18488/journal.8/2016.4.3/8.3.134.141.