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Dynamics of Economic Well-Being: Poverty 2009-2011

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Report Number P70-137


This report presents data on poverty based on information collected in the Survey of Income and Program Participation (SIPP). The report describes patterns of poverty using measures with different time horizons and provides a dynamic view of the duration of poverty spells and the frequency of transitions into and out of poverty. It further examines how poverty dynamics vary across demographic groups. The report focuses on data collected in the 2008 Panel of the SIPP over the period of January 2009 to December 2011 and, where appropriate, makes comparisons to data collected for January 2005 to December 2007 in the 2004 SIPP Panel. See Text Box 1 for a detailed discussion of data sources and reference periods covered in this report.

The SIPP allows policy makers, academic researchers, and the general public to paint a more detailed portrait of poverty than the one provided by the official annual poverty estimate. The official annual poverty rate, based on the Current Population Survey Annual Social and Economic Supplement (CPS ASEC), captures a snapshot of well-being at a single time period. Once a year, the CPS ASEC measures the percentage of people whose annual family money income falls below their official poverty threshold but does not address how poverty varies across shorter or longer time periods or how an individual’s poverty status may change over time.1 Compared with the official annual poverty rate, longitudinal research finds poverty rates vary by the time period examined—a small fraction of people are in poverty for more than 1 year, while a larger percentage of people experience poverty for shorter time periods.2

The SIPP interviews a representative sample of U.S. households every 4 months. The population represented (the population universe) is the civilian noninstitutionalized population of the United States. Core content of the SIPP identifies demographic characteristics, labor force participation, government program participation, and various income sources for members of sampled households.

Poverty statistics presented in this report adhere to the standards specified by the Office of Management and Budget’s Statistical Policy Directive 14. The Census Bureau uses a set of money income thresholds that vary by family size and composition to determine who is in poverty. If a family’s total income is less than that family’s threshold, then that family and every individual in it are considered to be in poverty. The poverty thresholds do not vary geographically. They are updated annually to reflect changes in the cost of living using the Consumer Price Index (CPI-U).3

Since SIPP respondents are interviewed throughout the year and asked about their income for the previous 4 months individually, each month’s poverty status is determined by comparing monthly income to the appropriate monthly poverty threshold. Monthly thresholds are calculated by multiplying the base-year annual poverty thresholds by an inflation factor relevant to the reference month and then dividing the calculated annual threshold by 12.

This report discusses poverty rate estimates for different time periods, measures the length of time people remain poor, and follows the movement of people into and out of poverty. The poverty measures discussed include monthly, annual, episodic, and chronic poverty rates. To capture changes in poverty status over time, the report examines poverty entry rates, poverty exit rates, and the duration of poverty spells. See Text Box 2 for a more detailed description of each measure used in this report.


  • Over the 36-month period from January 2009 to December 2011, 31.6 percent of the U.S. population was in poverty for at least 2 months, an increase from 27.1 percent over the period of 2005 to 2007.4
  • The percentage of people in poverty all 36 months from 2009 to 2011 was 3.5 percent, an increase from 3.0 percent over the period of 2005 to 2007.
  • By 2011, 5.4 percent of people who were not in poverty in 2009 had entered poverty.
  • Of individuals in poverty in 2009, 12.6 million (35.4 percent) were not in poverty in 2011, but approximately half of those who exited poverty continued to have income less than 150 percent of their poverty threshold.
  • For individuals experiencing a poverty spell lasting 2 or more consecutive months from 2009 to 2011, an estimated 44.0 percent of poverty spells ended within 4 months, while 15.2 percent of spells lasted more than 2 years.
  • From 2009 to 2011, the median length of a given poverty spell was 6.6 months, up from a median length of 5.7 months over the period of 2005 to 2007.

1 See Source of Data on page 14 for a discussion of the differences in annual poverty rates across the SIPP and CPS ASEC.

2 Examples of previous longitudinal studies on poverty include: Robin J. Anderson, “Dynamics of Economic Well-Being: Poverty, 2004–2006,” Current Population Reports, Series P70-123, U.S. Census Bureau, Washington, DC, 2011. Stephanie R. Cellini, Signe-Mary McKernan, and Caroline Ratcliffe, “The Dynamics of Poverty in the United States: A Review of Data, Methods, and Findings,” Journal of Policy Analysis and Management 27 (2008), pp. 577–605. John Iceland, “Dynamics of Economic Well-Being: Poverty, 1996–1999,” Current Population Reports, Series P70-91, U.S. Census Bureau, Washington, DC, 2003. Mary Naifeh, “Dynamics of Economic Well-Being, Poverty, 1993–94: Trap Door? Revolving Door? Or Both?,” Current Population Reports, Series P70-63, U.S. Census Bureau, Washington, DC, 1998. Signe-Mary McKernan and Caroline Ratcliffe, “Transition Events in the Dynamics of Poverty, Urban Institute Research Report,” 2002, <www.urban.org/url.cfm?ID=410575>. Mary Jo Bane and David Ellwood, “Slipping Into and Out of Poverty: The Dynamics of Spells,” Journal of Human Resources 21 (1986), pp. 1–23. Ann Huff Stevens, “The Dynamics of Poverty Spells: Updating Bane and Ellwood,” AEA Papers and Proceedings 84 (1994), pp. 34–37. Ann Huff Stevens, “Climbing Out of Poverty, Falling Back In: Measuring the Persistence of Poverty Over Multiple Spells,” Journal of Human Resources 34 (1999), pp. 557–88.

3 For additional information on how the Census Bureau measures poverty see <www.census.gov/hhes/www/poverty/about/overview/measure.html>.

4 The estimates in this report (which may be shown in text, figures, or tables) are based on responses from a sample of the population and may differ from the actual values because of sampling variability or other factors. As a result, apparent differences between the estimates for two or more groups may not be statistically significant. All comparative statements have undergone statistical testing and are significant at the 90 percent confidence level unless otherwise noted.

Page Last Revised - October 8, 2021
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