Robert Sampson writes in today's NYT Op-Ed page:
...evidence points to increased immigration as a major factor associated with the lower crime rate of the 1990's (and its recent leveling off).
Hispanic Americans do better on a range of various social indicators -- including propensity to violence -- than one would expect given their socioeconomic disadvantages. My colleagues and I have completed a study in which we examined 8,000 Chicago residents who were asked about the characteristics of their neighborhoods.
Surprisingly, we found a significantly lower rate of violence among Mexican-Americans than among blacks and whites...Indeed, the first-generation immigrants (those born outside the United States) in our study were 45 percent less likely to commit violence than were third-generation Americans, adjusting for family and neighborhood background. [TC: But don't absolute probabilities play the key role here? And should we compare Mexicans to "blacks and whites" or to each group in isolation?] Second-generation immigrants were 22 percent less likely to commit violence than the third generation.
Our study further showed that living in a neighborhood of concentrated immigrants is directly associated with lower violence (again, after taking into account a host of factors...)
Alas, there is no permalink these days. Here is the relevant project which generated the data. No one of Sampson's pieces on his web page seems to cover this result, though many are relevant more broadly. Also see this summary of his criticism of "broken window" and "tipping point" theories of crime.
Here is another piece which seems to support the basic result that Mexican immigration lowers crime. Here is a survey article on the topic. This piece (see p.113) suggests that crime is lower in border cities than comparable non-border cities, and that Mexican immigration cannot be identified as a cause of a higher U.S. crime rate.
Yes comments are open, but purely anecdotal accounts of how you were once mugged by a Mexican, or how your neighborhood just isn't "the same anymore" are discouraged. I'm posting a version of this over at MarginalRevolution.com as well, look for the differing comments.