A study by the Pew Research Center shows an increase in residential segregation. What does this mean? Divide all U.S. households into three groups by median income—those between $34,000 and $104,000 and the two groups outside that range. Paul Taylor, the Center’s executive vice president, says the middle group has shrunk, which is increasing the gap between the two ends of the spectrum. The three cities that have seen the greatest segregation by income are Houston, Dallas and San Antonio. Taylor can’t say for certain what it is about Texas, but thinks the Sunbelt might have something to do with it. Retirees are attracted to the well-to-do neighborhoods, while workers from south of the border are attracted by the lower-end service jobs.