Fig. 1From: Radiological research activity 1998–2007: relationship to gross domestic product, health expenditure and public expenditure on educationTrend of the cumulative impact factor (IF) between 1998 and 2007 shown separately for different groups of gross domestic product per capita (GDP p.c.). Note that the USA graph is separately shown with a differenty-axis because of the much larger cumulative IF in comparison with all other countriesBack to article page