I hadn't seen this before.
But these are the very residents notoriously averse to responding to census inquiries, regardless of assurances that being counted won’t lead to an unwelcome knock on the door from the cold-hearted immigration heavies at ICE. “Irregular” migrants have a vested interest in remaining invisible. Should you ask a crowd of such people, “Who’s not supposed to be here?” funnily enough nobody’s likely to raise a hand. . . .
As the study’s authors anticipated arriving at a number well below that eternally unchanging 11.3 million, confirmation bias alone would have helped produce a lowball estimate. Instead, even with all the inputs rigged at improbably low levels, the model still generated a population of illegal immigrants in the US of 16.7 million — 50 percent higher.
At first I wondered whether the column in the NY Post summarized the study accurately. It appears it did: "Yale Study Finds Twice as Many Undocumented Immigrants as Previous Estimates".
But as one would suspect the study has been criticized.
Here is a recent study that seems mostly supportive.