Understanding Poverty: Definition, Causes, and Measurement

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Poverty is the condition of lacking enough income or resources to meet a minimum standard of living: adequate food, shelter, clean water, clothing, health care and, in most modern definitions, basic education. Economists and statistical agencies turn that idea into a measurable line, usually an income threshold. Anyone whose resources fall below the line is counted as poor. The line, the resources counted and the unit being measured (a person, family or household) all vary by country and by method, so two official figures can describe the same population differently.

What poverty means

The core meaning of poverty is a shortfall: what a person or household has is less than what it needs. The disagreement among definitions is about what “needs” means.

Absolute poverty sets a fixed standard, such as the cost of food, shelter and other essentials needed to survive. The standard is adjusted only for price changes, so it measures whether people can buy the same basic bundle over time. The U.S. official measure and the World Bank’s extreme poverty line are both absolute measures.

Relative poverty defines being poor in comparison with the rest of society. A common approach counts people living on less than a set share of median household income, often 50% or 60%, adjusted for household size. The European Union’s “at risk of poverty” indicator uses 60% of national median equivalized disposable income. Under a relative measure, poverty can persist even as everyone’s real income rises, because the line rises with the median.

Extreme poverty refers to the most severe deprivation, where people cannot reliably secure food, safe water or shelter. Internationally, it is measured against the World Bank’s line, currently set at $3.00 per person per day.

Multidimensional poverty treats income as only one part of the picture. A household may report income above the line and still lack electricity, clean water, schooling or health care.

Poverty is also described by its duration. Situational poverty follows a specific event, such as a layoff, divorce, medical emergency or natural disaster, and may be temporary. Generational poverty passes from parents to children. Systemic poverty refers to poverty that persists because of how institutions work: laws, labor markets, housing policy, school funding or discriminatory practices that keep certain groups from building income and assets.

How poverty is measured

Income thresholds and the poverty line

Most national measures follow the same logic:

1. Define a minimum basket of goods and services.
2. Price that basket, which gives the poverty line.
3. Adjust the line for family size and composition.
4. Compare each unit’s resources with its line.
5. Update the line each year for inflation.

The choices made at each step decide who counts as poor. A line based on pretax cash income treats a family receiving food assistance the same as one that receives nothing. A line adjusted for local housing costs can reclassify families in expensive cities as poor.

The U.S. official poverty measure

The U.S. official measure dates to the 1960s. Economist Mollie Orshansky at the Social Security Administration built the original thresholds by taking the cost of a minimal food plan and multiplying it by three. That multiplier reflected survey evidence that families then spent about a third of their income on food. The thresholds have since been carried forward mainly by adjusting for inflation with the Consumer Price Index for All Urban Consumers (CPI-U), not by repricing the basket.

The Census Bureau publishes thresholds that vary by family size and by the number of related children under 18, with separate values for some households headed by people 65 and older. The measure compares a family’s pretax money income (wages, Social Security, cash assistance and similar cash sources) with its threshold. If the family’s income is below the threshold, every member of that family is counted as in poverty. Noncash benefits such as food assistance and housing subsidies are not counted, and neither are taxes or tax credits.

People whose poverty status cannot be determined from family income fall outside the poverty universe: people in institutions such as prisons and nursing homes, in military barracks or in college dormitories, and unrelated individuals under 15, such as foster children, whose income is not asked about.

The national poverty rate is the number of people below their thresholds divided by the number of people whose poverty status can be determined. The Census Bureau publishes the official rate each year from the Current Population Survey Annual Social and Economic Supplement (CPS ASEC).

Thresholds vs. guidelines

Census poverty thresholds are a statistical tool used to count the poor. HHS poverty guidelines are a simplified version used to set eligibility for programs. Many programs set eligibility as a percentage of the guidelines, such as 130% or 200%, so a household can qualify for aid while sitting above the official poverty line. The two sets of numbers are close but not identical, and people often confuse them.

The Supplemental Poverty Measure

Since 2011, the Census Bureau has also published the Supplemental Poverty Measure (SPM). It addresses several weaknesses of the official measure. It adds noncash benefits and refundable tax credits to resources, and it subtracts taxes, work expenses, child care and out-of-pocket medical costs. It adjusts thresholds for differences in housing costs across regions and bases them on recent spending on food, clothing, shelter and utilities. The SPM does not replace the official measure. It shows how much government programs and necessary expenses change the count.

The international poverty line

The World Bank builds its international poverty line from national poverty lines in low-income countries, the value of the basic needs of one adult, and converts them into a common unit using purchasing power parity (PPP), because a dollar exchanged at market rates buys far more in some countries than in others. The line is revised when new price data arrive, which is why its dollar value has changed over the decades and why poverty counts from different revisions are not directly comparable.

Multidimensional measures

The Global Multidimensional Poverty Index, developed by the UN Development Programme and the Oxford Poverty and Human Development Initiative, scores households on ten indicators across three areas: health, education and living standards. The indicators include nutrition, child mortality, years of schooling, school attendance, cooking fuel, sanitation, drinking water, electricity, housing and assets. A person is counted as multidimensionally poor if deprived in at least a third of the weighted indicators. This approach captures households that are poor in services and infrastructure even when cash income is hard to measure.

Worked example: incidence vs. magnitude

The share of people who are poor (poverty incidence) and how far below the line they fall (poverty magnitude, or depth) are different questions. A hypothetical example shows why.

Hypothetical: a village of 10 people, a poverty line of $20 per day, and these daily incomes: $5, $10, $15, $18, $25, $30, $40, $50, $60 and $100.

Headcount ratio (incidence). Four people earn below $20.

Headcount ratio = poor people ÷ total population = 4 ÷ 10 = 40%

Poverty gap index (depth). For each poor person, compute the shortfall as a share of the line. Non-poor people count as zero.

Poverty gap index = (0.75 + 0.50 + 0.25 + 0.10) ÷ 10 = 1.60 ÷ 10 = 16%

The total dollar shortfall is $32 per day. In theory, that is the minimum transfer needed to lift everyone to the line, assuming perfect targeting and no change in behavior.

Squared poverty gap (severity). Squaring each ratio gives more weight to the poorest: (0.5625 + 0.25 + 0.0625 + 0.01) ÷ 10 = 0.0885.

Now give $3 per day to one person and compare two choices:

• Give it to the $18 earner. That person reaches $21. The headcount falls to 30%, and the squared gap falls only to 0.0875.
• Give it to the $5 earner. That person reaches $8. The headcount stays at 40%, but the squared gap falls to about 0.0683.

The same $3 lowers incidence in the first case and severity in the second. A policy judged only on the headcount rate rewards helping people just below the line, which is why analysts report depth and severity alongside the rate.

The same mechanics apply to a household threshold. Hypothetical: a family of four with two children has a threshold of $32,000 and pretax money income of $28,000. Its income-to-poverty ratio is 28,000 ÷ 32,000 = 0.875, so all four members are counted as poor. Even with $5,000 in food and housing assistance, the official measure would still count it as poor; the SPM would add those benefits to resources.

Causes of poverty

Poverty rarely has a single cause. Explanations usually combine individual circumstances with economic and institutional conditions.

Economic conditions. Weak job growth, recessions, low wages relative to living costs and a high cost of housing, food or health care can push working households below the line.

Shocks. Illness, disability, the death of an earner, divorce, natural disasters and price surges can tip a household into poverty. Mental health problems and addiction can be both a cause and a consequence. The World Bank estimated that the COVID-19 pandemic pushed roughly 100 million additional people into extreme poverty.

Structural and institutional factors. Poor infrastructure, limited access to schooling, weak property rights, conflict and war, and thin social safety nets limit people’s ability to earn and save. Low access to land, capital and skills, the factors of production, limits what households can produce or earn.

Discrimination. Laws or practices that restrict access to jobs, housing, credit, education, health care or social services keep affected groups from reaching a decent standard of living. Social exclusion can isolate whole communities even without formal barriers. Groups often identified as facing this kind of disadvantage include Black, Indigenous and other people of color, women (including single mothers), LGBTQ+ people and people living with HIV/AIDS.

The poverty cycle. Poverty can reinforce itself. Children in poor households may attend underfunded schools, miss school because of illness, and enter adulthood with fewer skills and less family wealth to fall back on. Families that escape poverty can fall back in after a job loss, a food price spike or a climate-related disaster, because they have little savings to absorb the shock.

Effects of poverty

At the household level, poverty means difficulty securing food, clothing, shelter and medicine, along with higher stress and worse physical and mental health. The effects on children last longest: a higher risk of low birth weight, child mortality in the poorest countries many times that of high-income countries, and more missed school, made worse by homelessness. At the society level, high poverty rates are associated with slower growth, unemployment, poor educational outcomes, urban decay, crime and greater social tension.

How poverty is reduced

Approaches fall into two broad groups. Meeting immediate needs includes cash transfers, food assistance and housing support, clean water through wells and sanitation systems, clinics and hospitals, and emergency shelter and disaster relief. Raising earning capacity over time includes schools and job training, agricultural education that raises crop yields, roads and electricity that connect people to markets, labor policies such as minimum wages tied to living costs, paid leave and pay equity, and removing discriminatory barriers to jobs, housing and credit.

Over the long run, the largest declines in poverty have come with sustained economic growth, as in today’s developed countries after the Industrial Revolution, when higher productivity lowered the cost of goods and agricultural advances increased food supply. Growth in output, measured by GDP, creates room for higher wages and public services, though how widely gains are shared depends on policy. The World Bank, which leads international efforts with the United Nations, has set a goal of reducing extreme poverty to below 3% of the global population by 2030.

Limitations of poverty measures

• A single line creates a cliff. A family $1 above the threshold is counted as not poor, though its living standard is nearly identical to one $1 below.
• Income is not the whole story. Wealth, debt, access to services and household needs vary widely at the same income.
• Prices differ by place. The official U.S. measure uses the same thresholds nationwide, regardless of local housing costs.
• Inflation adjustment is only as good as the index. If CPI-U understates or overstates the cost of necessities for poor households, the line drifts.
• Survey coverage gaps. People who are homeless, institutionalized or hard to reach may be undercounted.
• Within-household inequality. Measures assume resources are shared equally among members, which may not hold.

Poverty vs. related terms

• Poverty vs. inequality. Inequality describes how income is spread across a population. A country can become more unequal while poverty falls, if the poorest gain but the richest gain faster.
• Poverty vs. low GDP per capita. GDP per capita is an average of national output. A country with a moderate average can still have high poverty if income is concentrated.
• Poverty vs. unemployment. Unemployment is a labor market status. The “working poor” have jobs but fall below the line, and a retiree can be out of the labor force without being poor.

The Bottom Line

Poverty figures matter to anyone reading economic data, judging public programs or checking eligibility for aid. Each number depends on the line chosen, the resources counted and the unit measured, so official rates from different methods can describe the same population differently. Reading incidence alongside depth and severity, and knowing which measure produced a figure, gives a more accurate picture than a single headcount rate.