Comparing data sources of real GDP in purchasing power parities

When comparing the development in international incomes, e.g. GDP per capita, the data used refer most often to incomes in real purchasing power parity (PPP) terms. The present analysis compares the most used data sources - Maddison's Historical Statistics, Penn World Table (PWT) and OECD - and includes four countries, the USA, Japan, the UK and France. These time-series data from the respective sources might be expected to be rather identical for a specific country, but the analysis reveals that there will be some differences, probably created by methodological procedures, which can influence, e.g. the very often applied unit root and cointegration tests of income convergence.