He collected and analyzed statistical indicators of economic performance of 14 countries in Europe, the U.S. and Japan for 60 years. Analysis of the materials led to the advancement of a number of hypotheses relating to various aspects of the mechanism of economic growth, concerning the level and variability of growth, structure of the GNP and distribution of labor, the distribution of income between households, the structure of foreign trade. Kuznets founded the historically grounded theory of economic growth. The central theme of these empirical studies is that the growth of the aggregated product of the country necessarily implies a profound transformation of the whole of its economic structure. This transformation affects many aspects of economic life – the structure of production, sectoral and occupational structure of employment, the division of occupations among family and market activities, the income structure, size, age structure and spatial distribution of the population, cross-country flows of goods, capital, labor and knowledge, the organization of industry and governmental regulation. Such changes, in his opinion, are essential for overall growth and, once started, shape, constrain or support the subsequent economic development of the country. Kuznets made a profound analysis of the impact on economic growth by demographic processes and characteristics.