Pew's baseline estimate of the number of Muslims currently in Europe — the estimate upon which its future projections are calculated — has been undercounted by at least five million Muslims.

The UCIDE figures — which posit that there are roughly 750,000 more Muslims in Spain today than the estimate proffered by Pew — are widely recognized in Spain as the most accurate assessment of the Muslim population in that country. It remains unclear why Pew failed to mention the UCIDE report in its source appendix.

In Germany, Pew "decided not to count" the one million plus Muslim asylum seekers who arrived in the country in 2015/2016 because "they are not expected to receive refugee status."

The Pew report entirely ignores the key issue of how Europe will integrate tens of millions of Muslim migrants whose values — including anti-Semitism, polygamy, female genital mutilation and honor violence — cannot be reconciled with those of Europe's Judeo-Christian and liberal-democratic heritage.

https://www.gatestoneinstitute.org/11545/how-many-muslims-in-europe