Poverty Line
What is Poverty Line?
A poverty line is an income or consumption threshold below which a household counts as poor, used to measure how much poverty a country has.
National poverty lines are usually built with the cost-of-basic-needs method: price a food basket that supplies a minimum calorie intake, then add an allowance for essential non-food items such as housing, fuel and clothing, and the sum is the line. Households whose income or consumption falls below it are counted poor, and the share of people below it is the headcount ratio. Most poor countries measure consumption rather than income, because farm and informal earnings are irregular and hard to report accurately. The World Bank also maintains international lines so countries can be compared, converting with purchasing power parity rates rather than market exchange rates and revising the level as price data are updated. Every line is a judgment call, and moving it a little moves the poverty count a lot.
Poverty Line: a worked example
Take a country pricing its national line. A diet meeting the minimum calorie standard costs 1,200 shillings per person per month. Among households that spend just enough to reach that food standard, non-food essentials come to another 800 shillings, so the poverty line is 2,000 shillings per person per month. A family of four needs 8,000 shillings a month to clear it; if the household spends 7,000, it sits below the line and every member is counted poor. Raising the line to 2,200 would push the family's requirement to 8,800 and pull in many households that were just above.
The mistake students make with poverty line
Students treat the poverty line as one worldwide number that neatly sorts the poor from the not-poor. Lines differ by country, get revised, and are drawn with different methods, so poverty rates from two sources are often not comparable. The deeper error is reading the line as a cliff: a household just above it is barely different from one just below. That is why economists also report the poverty gap, which measures how far below the line people fall.
Poverty Line questions
How is a poverty line calculated?
A poverty line is calculated by pricing the goods a household needs to avoid poverty, using survey data on what people actually buy. Statisticians find the spending level at which a household reaches a minimum calorie standard, then look at what households at that level spend on housing, fuel and clothing, and add the two together. Between rebuilds the line is only adjusted for inflation, which is why it drifts away from real living costs and has to be redrawn periodically.
Why do international poverty comparisons use purchasing power parity?
Purchasing power parity is used because market exchange rates understate what a currency buys in a poor country. Rent, food and local services are cheaper there, so converting incomes at market rates would make poverty look worse than it is. PPP conversion values incomes by what they actually buy, which makes cross-country counts meaningful.
What is the poverty gap?
The poverty gap measures how far below the line poor people fall, not just how many are below it. It is usually expressed as the average shortfall across the whole population, stated as a share of the line. Two countries can share a headcount ratio while one has people bunched just under the line and the other has people far beneath it.
Formula / Example
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