Analysts advance a number of theories to explain why the proportion of the U.S. population living in poverty fluctuates, but doesn't seem to decline overall -- despite years of economic good news. Some experts say that one factor is often overlooked: the impact of immigration.

As poor people keep flowing into the country, any possible improvements in the poverty data are neutralized.

• The proportion of the American population living in poverty was higher in 1998 than in 1973.

• Because many immigrants are relatively unskilled, their poverty rate is significantly higher at 18 percent -- compared to the 12.1 percent poverty rate for the native-born.

• Immigrants and their U.S.-born children make up 26 percent of the 35 million U.S. poor -- although this group makes up only 20.5 percent of the U.S. population.

Harvard University economist David J. Borjas estimates that the wage gap between high school dropouts and educated labor widened by 10 percentage points between 1979 and 1995. About half that increase may be due to the increased supply of labor resulting from immigration.

Source: Peter Brimelow, "Poverty's Roots," Forbes, August 21, 2000.