"During the 1980s, around 13% of Americans in their 40s spent at least one year, below the poverty line; in the 1990s, 36% of people in their 40s did." Source cited in article quotes the increase of poverty risk and income insecurity in the US since the 1970s. "In a rare study of vulnerability to poverty, Mr. Rank and his colleagues found that the risk of a plummet of at least a year below the official poverty line rose sharply in the 1990's...For all age groups except those 70 and older, the odds of a temporary spell of poverty doubled in the 1990's, Mr. Rank reported in a 2004 paper titled, "The Increase of Poverty Risk and Income Insecurity in the U.S. Since the 1970's," written with Daniel A. Sandoval and Thomas A. Hirschl, both of Cornell University. For example, during the 1980's, around 13 percent of Americans in their 40's spent at least one year below the poverty line; in the 1990's, 36 percent of people in their 40's did, according to the analysis." [NY Times article]. “Between the ages of 20 and 75, 58% of Americans will experience at least one year below the official poverty line, while 75% will encounter a year below 150% of the poverty line (Rank and Hirschl 1999c).” [Sandoval, Rank, Hirschl].
Source: Daniel A. Sandoval and Tomas A. Hirschl. You New York Times May 8, 2006, a 14 [Original study: Daniel A. Sandoval, Mark R. Rank, Thomas A. Hirschl, “The Increasing Risk of Poverty Across the American Life Course,” Demography 46, 4. (2009): 719, September 9, 2014, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2831356/.]