Some research even suggests that increases in immigration may partly explain the reduction in the U.S. crime rate. A 2005 study showed that immigration to large U.S. metropolitan areas does not increase, and in some cases decreases, crime rates there. A 2009 study found that recent immigration was not associated with homicide in Austin, Texas. The low crime rates of immigrants to the United States despite having lower levels of education, lower levels of income and residing in urban areas (factors that should lead to higher crime rates) may be due to lower rates of antisocial behavior among immigrants. A 2015 study found that Mexican immigration to the United States was associated with an increase in aggravated assaults and a decrease in property crimes. A 2016 study finds no link between immigrant populations and violent crime, although there is a small but significant association between undocumented immigrants and drug-related crime.