A question about a survey (Germans and Jews – United by their past, divided by their present?)

I came across a survey. You view it via this link.

There is something that makes me curious about this survey. Why were Germans, Israelis and Jews living in the US selected for interviews?

Why did people who conducted the survey thought that the comparison between these three groups was useful in order to reach the aim of their research project?
There are Jews living outside Israel and USA too.

Probably because about 85% of Jews live in Israel and USA. So it was easier to conduct the survey in those two countries, instead of adding a dozen more to capture that extra 10-12%.