Immigration responsible for lower crime rates?

A study published in last month in Social Science Quarterly by a Colorado University professor must be driving the anti-immigrant zealots crazy. This is from a story on the website ScienceDaily:

ScienceDaily (May 13, 2010) — During the 1990s, immigration reached record highs and crime rates fell more precipitously than at any time in U.S. history. And cities with the largest increases in immigration between 1990 and 2000 experienced the largest decreases in rates of homicide and robbery, a University of Colorado at Boulder researcher has found.

Tim Wadsworth, an assistant professor of sociology, has tested the hypothesis, famously advanced by Harvard sociologist Robert J. Sampson, that the rise in immigration could be related to the drop in crime rates….

‘Cities that experienced greater growth in immigrant or new-immigrant populations between 1990 and 2000 tended to demonstrate sharper decreases in homicide and robbery,’ Wadsworth writes. ‘The suggestion that high levels of immigration may have been partially responsible for the drop in crime during the 1990s seems plausible….’

Wadsworth’s research suggests that, controlling for a variety of other factors, growth in the new immigrant population was responsible, on average, for 9.3 percent of the decline in homicide rates, and that growth in total immigration was, on average, responsible for 22.2 percent of the decrease in robbery rates.”