"Charitable giving in the U.S. as a proportion of gross domestic product, for example, is around 1.7%. In Europe, it is around 0.7% and in Japan it is just 0.04%, according to U.S. wealth manager Northern Trust."

GDP is a very similar statistic to GNI, but also includes income from other countries such as interest and dividends. Per capita rankings would make both Japan and Europe as a whole look even worse, since the the US has a higher per-capita GPD. For Sweden, which has a comparable GDP per person, it would come out about the same.