Safiullin, M. R., L. A. Elshin, and E. G. Nikiforova. “Methodological Approaches to the Diagnosis and Forecast of the Long-Wave Fluctuations in the Economy”. International Journal of Economics and Financial Issues, vol. 6, no. 4, Oct. 2016, pp. 1616-24, https://www.econjournals.com/index.php/ijefi/article/view/3028.