N.D. Kondratiev's technological waves and GDP dynamics

The article begins with an overview of theoretical works on the existence of cycles in the process of economic development and publications describing econometric models of long waves. The article shows that the main trend in GDP dynamics, corresponding to internal economic processes rather than the influence of exogenous factors, can be described by a superposition of Kondratiev's long waves represented by sinusoidal functions. The parameters of each of these waves - the beginning of its origin, the amplitude and two more parameters specifying its dynamics - allow one to "tune" the model to the dynamics of GDP in different countries with different GDP sizes, different beginnings of a particular wave and their different periods. The models for six European countries: Italy, Spain, Portugal, Norway, Finland and Sweden, as well as for the USA, based on GDP values, measured in international dollars, are constructed. Taking into account the generally accepted opinion on the existence of five long waves from the end of the 18th to the end of the 20th century, estimates of the beginning time of each of these waves, the values of their amplitudes, the length of their periods, as well as the characteristics of the entire set of waves as a whole are obtained for each of the specified countries. It is shown that there are both similarities in the structure and dynamics of N.D. Kondratiev's long waves in these countries, and differences in the moments of their origin, development and withdrawal into the "second" plan. Based on the constructed models, an assessment is given of the magnitude of deviations of GDP values from the model during periods of wars, economic crises, etc.