I would never trust a report like that. Look at the "sources and methodology" section on page 6 in the PDF.
We know they used some types of sources and that they interviewed some people.
We do not know:
How the individual sources contributed to the final calculation.
What their selection criteria were when they processed the sources.
The qualitative aspects of their interview process. "Interviews" can be done in many ways, so we need to know how.
Where to find these sources so that we can read them ourselves, discover if we are dealing with data from politically motivated actors, verify that the sources use proper methods, etc.
The actual period of analysis. Let's assume it runs from 1 January 2015 to 31 December 2015? But really, they could have mentioned it.
There is more stuff elsewhere that we do not know. Stuff about France, for example.
The large outflow of millionaires from France is notable – France is being heavily impacted by rising religious tensions between Christians and Muslims, especially in urban areas. (p. 4)
They never substantiate what "heavily impacted" means in terms of concrete facts or even numbers.
We are furthermore never informed of the relation between that statement and the numbers they present, except that (p. 3):
We interviewed migration experts and HNWIs to find out on their reasons for leaving. Notable reasons that they mentioned included: 1) Paris: Rising religious tensions, lack of opportunities.
No qualitative information is given for the rest of the country. See, here it would have been nice if they had not left out vital information about their interview methods so that we could know how they interviewed people. Was just 1 answer received as to why they moved, or were they able to list off multiple questions? If they could only give 1 answer, what would be the rationale for that and how can we be sure they really expressed what's most important to them? If they could list off several answers, did the researchers quantify the interview answers to find the most popular reason given? If they did that, why can't we know the other popular reasons?
The fact that no qualitative information is given for the rest of the country is also an important distinction, because note the phrase on p. 4: "...especially in urban areas."
I guess they mean Paris, and practically just Paris. Here's why:
According to themselves, there were 323,000 millionaires in France in 2015 (p. 4).Of these, 126,000 or 39% lived in Paris (p. 3). Yet, France had an outflow of 10,000 millionaires for the entire year (p. 4) and 7,000 of these or 70% lived in Paris (p. 3). The rest of the many urban areas in that big nation and the rural areas have to split the last 30% that account for millionaire outflows that year, which doesn't really leave much for each place.
If we had to generalize, we would have to say that even though all of these people do leave the country France, it is mostly specifically Paris they are leaving from.
...I wish we had a way of knowing what reasons those other 30% of the millionaires, the ones not leaving Paris, had for leaving. We could have compared their answers to those in Paris.
Now, I feel a little odd reading that all of these Parisian millionaires leave because of tensions between Muslims and Christians or terrorism or whatnot when the UK ranks first s their destination of choice (the place in Europe where most people have died from terrorism in the last 20 years IIRC), and Israel, of all places, ranks 5th as their most popular destination.
It makes me wonder why we can't know whether the interviewers asked them why they chose to move to these places, in light of whatever reason they gave for moving in the first place?
I just feel like there's so many logical holes in this report that I'd never want to refer to it as a source of facts. It looks like some pretty sloppy work.