@Berenger, the above posted surveys show that descendants are not better integrated than the first generation, but worse. Meaning the group of people believing in fundamentalist and radical Islam is growing. This is a well-known fact in sociology and studies of religion, that the young generation are turning more towards their roots, especially second and third generation immigrants, who feel burdened by identity loss. Especially if the number of immigrants are allowed to be so high that we see the emergence of self-perpetuating parallel societies in certain areas, as we have.
Also, your criticism of statistics is a general one. I can only say that most everyone, including most of the sciences, rely to a high degree on statistical data, and that a multitude of surveys demonstrate the same trends.
A survey dealing with other parts of Europe.
The German research institute WZB in cooperation with the Dutch sociologist Ruud Koopmans made in December 2013 a survey based on 9.000 European Muslims with Turkish or Morrocan backgground in Germany, France, Holland, Belgium, Austria and Sweden. When presented with a series of statements, 60% of the respondents agreed that 'all Muslims must return to the roots of Islam', 75% that 'there is only 1 interpretation of the Quran, which all Muslims must adhere to', and 65% that 'religious rules are more important than secular laws'. 44% of the respondents declared themselves in agreement with all three statements.