Supporters of massive and illegal immigration frequently use economic studies to mislead. Sometimes the studies themselves are misleading, such as using bogus methodologies. However, mostly the studies are just used to come to misleading conclusions. Some of the ways they mislead or are used to mislead include:

* Lumping all forms of immigration together and ignoring the large differences between low-skilled and high-skilled immigration...

* Bribery, sometimes using fantastical amounts of money, and sometimes using very small amounts of money...

* Using absurd methodologies...

* And, last but not by any means least, ignoring all the costs of massive immigration. For instance, promoters of a study will claim that massive immigration has a low cost or that it represents a gain. What those promoters will fail to note is that the study they're promoting only discussed direct fiscal costs. No study has ever tried to put a price tag on all the indirect fiscal costs and all the non-fiscal costs. For instance, higher immigration does drive some Americans out of work, and some of those go on to commit crimes they would not have otherwise committed. Those crimes (and any resulting incarceration, increased welfare use by relatives of the perpetrator, and so on) have a cost which economic studies don't include in their balance sheets. Massive low-skilled immigration gives even more political power to the far-left, and that too has a cost to the great majority of Americans who aren't in the far-left. It also gives more power inside the U.S. to foreign countries, such as the Mexican government (see the hundreds of posts at that link). Massive immigration also takes political power away from native-born Americans, and not just as naturalized citizens vote but also since a small number of illegal aliens do vote and especially since illegal aliens count towards Congressional representation. Some supposed U.S. legislators occasionally represent the interests of foreign citizens (see Gil Cedillo, Antonio Villaraigosa, and Martin Sandoval for starters); that has a cost. And, the main reason illegal immigration is allowed is because our elites are corrupt: they hope to benefit in one way or another from illegal immigration whether monetarily or electorally. Our elites being corrupt has a huge, non-fiscal cost to the U.S. and leads those elites to promote policies that don't serve the interests of the great majority of Americans. No economic studies of immigration include all of those and more as costs.