I read the percentages of losses per population were
Greece 10% Soviet Union 2.8% Holland 2.2% France 2% Poland 1.8% Yugoslavia 1.7% Belgium 1.5%
Are these numbers correct? Thanks in advanced.
No, Poland did, Poland lost 5.5-6 million people dead out of a pre-war population of around of around 35 million, meaning that around 16% of its total population were killed between 1939 and 1945.
http://en.wikipedia.org/wiki/World_War_II_casualties#Total_deaths
The soviet union lost way more than 3%, where are you getting your figures?
If you want to go by ethnic group not nation, then over 50% of Europe's Jews were killed in WWII, across all nations.