IN AN attempt to lend empirical heft to his assertion that America has become "a dumping ground" for Mexico's criminal element, Donald Trump, a billionaire landlord and Republican presidential candidate, pointed to the case of Juan Francisco Lopez Sanchez, an undocumented Mexican national, who is accused of murdering a 32-year-old white woman last week in San Francisco. "This senseless and totally preventable act of violence committed by an illegal immigrant is yet another example of why we must secure our border immediately," Mr Trump said. It ought to be unnecessary to say that Mr Sanchez is not representative of Mexican immigrants, documented or undocumented. However, in light of the startling success of Mr Trump's message of fear, it seems many still need some convincing that such claims are specious. As it happens, a swift glance at the data handily undermines Mr Trump’s case that Latin American immigrants are prone to crime.

America's major cities, and the country as a whole, have seen a significant decline in rates of violent and property crime over the past 30 or so years. Crime has fallen even as the proportion of Americans born on foreign soil has grown, and as rates of unauthorised immigration have gone up, as illustrated by these graphs from the Immigration Policy Center.

This is not to say that rising immigration caused crime to go down, though some criminologists think the two trendsare related. No one knows for sure what combination of factors led to America's happy slide in crime rates. But there is little indication that the surge in immigration from the 1990s to the late 2000s, largely from Mexico and Central America, contributed to an increase, or retarded the decrease, in crime. According to Jörg Spenkuch, an economist at Northwestern University, increased immigration may have been associated with a barely statistically significant uptick in property crime, but crunching the numbers turns up "essentially no correlation between immigrants and violent crime".

Indeed, Robert Sampson, a sociologist at Harvard, has found that "increases in immigration and language diversity over the decade of the 1990s predicted decreases in neighborhood homicide rates in the late '90s and up to 2006." An eight-year study of violence in Chicago led Mr Sampson to conclude that Mexican immigrants are less prone to violence than native-born Americans, whites or black, of comparable age and socio-economic status. In recent years, El Paso, Texas has had the lowest murder rate of any American city with a population of 500,000 or more, despite sitting directly across the Rio Grande from Juarez, a Mexican city plagued with horrific gang violence. Other metropolitan magnets for new arrivals from south of the border, such as San Diego, San Antonio and Phoenix, are similarly pacific. "Cities of concentrated immigration are some of the safest places around," Mr Sampson observes.

These patterns are reflected, as one would expect, in data on incarceration rates. White men born in America are twice as likely to end up in prison as men born abroad, while American-born black men are many times more likely to land in jail than their immigrant counterparts. As a general matter, individuals with less education are more likely to get locked up. Nevertheless, immigrants from El Salvador, Guatemala and Mexico, who tend to be relatively unschooled, are put behind bars at lower rates than white Americans who didn't make it to graduation. In fact, American white guys with high-school diplomas are more likely to get tossed in the can than Guatemalan or Honduran fellows without them.

It's worth pointing out, as immigration opponents are quick to do, that incarceration rates jump considerably for the American-born children and grandchildren of immigrants. Thus, the incarceration rate of the American children and grandchildren of Mexican immigrants is about twice that of native-born non-Hispanic whites, and about half that of native-born blacks. It's an interesting and puzzling fact that certainly deserves attention when considering the effects of immigration and the challenges of assimilation. What it's not is evidence of the criminality of immigrants.

Mr Trump has claimed that "[w]hen Mexico sends its people, they’re not sending their best". Yet the evidence suggests that the people America has been taking in are truly and remarkably civil. If not the best, they're awfully good. Undocumented killers such as Mr Sanchez may inflame the xenophobic imagination, but America's violent criminals are much more likely to be home-grown than imported.

It makes sense that people with the gumption to uproot their lives to build better ones in a strange new land will be inclined to work hard and play by the rules. Undocumented immigrants have even more at stake; the lightest brush with the law can get them deported. When your correspondent lived in Houston, it seemed he was always getting stuck in traffic behind pick-up trucks laden with heavy lawn equipment. It wasn't that they were weighed down by their loads, or couldn't take a fast corner without losing a leaf-blower. It's just that Mexican landscapers are very careful to observe the speed limit. The inconvenience of such painstaking lawfulness is a more common symptom of America's immigration "problem" than crime. If Mr Trump cared to be accurate, he would be complaining about an infestation of upright drivers on their way to work.