That is a good question, and one that needs to be answered, but sadly it's not going to be touched for fear of accusations of racism or prejudice against Islam,

That is a good question, and one that needs to be answered, but sadly it's not going to be touched for fear of accusations of racism or prejudice against Islam, etc. So the general response from the left is to ban collecting any statistics which might reveal group differences, or to ban publication of such statistics if they are collected, or to assume that any such difference are the results of oppression if they are published. Which is a shame because Europe desperately needs to find a way of integrating these populations, and pretending that there is no problem is just sticking your head in the sand.