The article discusses the methodology and organization of statistical observation of the level of countries’ economic development. The theoretical basis of international comparisons is singled out and on its basis the comparative evaluation of inconsistency of theoretical positions and the reasons of differences of GDP growth is carried out. Based on the complexity of the formation of homogeneous data sets in order to obtain correct comparison results, a general scheme for the relationship between the theoretical base of international comparisons and PPP constraints is defined. The possibility of obtaining a single measurement of the indicators of national economies based on the existing sampling errors, measurement uncertainties and classification errors is considered. The emphasis is placed on combining the work using the ICP and CPI with the aim of achieving comparability of data in the territorial and temporal cross-section. Using the basic characteristics of sustainable economic growth, long-term prospects for changing the ranking positions of countries with different levels of income are determined. It is shown that the clarity and unambiguity of the theoretical provisions is the defining condition for the further process of data collection and formation of correct analytical conclusions.