Angela Unna Chukwu and  Samuel Oluwafemi Oyamakin,  On Hyperbolic Gompertz Growth Model.   journal   = {International Journal of Environmental and Ecological Engineering}, [online]. World Academy of Science, Engineering and Technology.
    May 2015, vol. 99(3). 189 - 193
    [viewed 27 February 2020]. Available from: https://publications.waset.org/pdf/10001343.