But let's face it: Any measures that include rewards and sanctions, gold stars and interventions, praise and embarrassment, even determinations about the future of entire institutions and those who work in them -- any and all such measures invite tampering by those who have reason to seek better results than the plain truth reveals.
The results change a little whether you use nominal GDP per head (ie, just the plain numbers ) or PPP adjusted (to take account of different price levels) but the are a number of countries in Europe with higher GDP per capita than Germany.