It’s an undeniable statistical fact openly clear to anyone with their eyes open. Have you ever been to Boro Park, Williamsburg, Monroe, New Square, Yerushalayim, Bnei Brak, Antwerp, etc. today compared to 15 years ago? They’re bursting at their seams. KJ is in the legal process of doubling their territory (they’ve already more than tripled their population in their existing territory) and have obtained government approval to tapping NYC’s water supply since their rural county supply is incapable of supporting their population. These places are doubling and more their population in a small timeframe. You can look at U.S. and Israeli censuses for these exclusively Yiddish-speaking towns or you can look at academic studies such as the aforementioned Avi Chai or you can simply look around the block. Living out-of-town makes it easy to miss the explosive population-growth that’s going on in the Jewish world today.
New York’s Chasidic schools student-body alone has grown 110% (i.e. more than double) from a mere 15 years ago. Satmar alone now has more school children than the entire Boston Public School system.