WASHINGTON - The increase in the number of people without health insurance has occurred largely because of illegal immigration, a study found. Researchers at the RAND Corporation, a nonpartisan think tank, analyzed data received from about 2,400 people in Los Angeles County in 2000 and 2001, and applied that information to the nation's undocumented population at large. The number of uninsured adults in the United States grew by about 8.7 million between 1980 and 2000. If the trend for Los Angeles County held true for the rest of the country, about a third of that growth can be attributable to...