Measuring GDP
AdvancedGross domestic product is the market value of final goods and services produced locally over a period, computable from the production (value-added), expenditure and income approaches. Nominal figures are distorted by price changes; real figures remove them, factor-cost valuation removes indirect taxes and subsidies, and per-capita figures aid comparison.
- National income is the collective name for aggregates such as GDP and gross national income
- GDP can be computed from the production (value-added), expenditure and income approaches — conceptually the same total
- Expenditure approach: private consumption ＋ investment ＋ government expenditure ＋ exports − imports
文體小知識：經濟現象說明文——說明本地生產總值的三個計算層面與名義實質之分，並以數字演算示範量度方法。
§Text Passage
1National income is the collective name for the statistical aggregates measuring an economy's performance, including gross domestic product and gross national income. Gross domestic product (GDP) is the market value of the final goods and services produced within the economy over a period; counting only final output avoids double-counting the value of intermediate inputs and overstating the economy's size.
2GDP is computed from three approaches. The production (value-added) approach sums the value added of every industry — output value minus the cost of intermediate inputs. The expenditure approach adds private consumption expenditure, investment expenditure, government expenditure and net exports. The income approach sums the wages, rent, interest and profit earned in production. All three measure the same total from different angles.
3Nominal GDP is valued at current market prices and moves with both output and prices; real GDP is valued at fixed prices, stripping out price changes to reflect actual output. Comparisons of performance must use real figures; dividing by population gives per-capita figures convenient for cross-economy comparison, and valuation at factor cost removes the effects of indirect taxes and subsidies.
4The GDP growth rate is computed on real figures and is the basic indicator of expansion or contraction; governments frame budgets and firms plan investment on it. Learning to compute and read these figures correctly is the foundation for the next lesson, which compares living standards and examines the limitations of national income statistics.
1Summary 重點摘要
Gross domestic product is the market value of final goods and services produced locally over a period, computable from the production (value-added), expenditure and income approaches. Nominal figures are distorted by price changes; real figures remove them, factor-cost valuation removes indirect taxes and subsidies, and per-capita figures aid comparison.
2Vocabulary cards Vocabulary
The collective name for aggregates such as gross domestic product and gross national income.
The market value of final goods and services produced within the economy over a period.
Output value minus the cost of intermediate inputs; the sum of value added across stages equals the value of the final product.
Goods and services bought by end users, not resold or further processed — only these are counted in GDP.
Computing GDP as private consumption expenditure plus investment expenditure, government expenditure and net exports.
GDP valued at current market prices, moving with both output and price changes.
GDP valued at fixed base-period prices, removing price changes to show movements in actual output.
The price index converting nominal GDP into real GDP: real equals nominal divided by the deflator times 100.
GDP after removing the effects of indirect taxes and subsidies on prices, reflecting what factors of production actually earn.
GDP divided by population, removing the effect of population size for easier comparison across economies.
3Step by step Steps
- Step 1: National income and GDPNational income is the collective name for the aggregates measuring an economy's performance, including gross domestic product and gross national income. GDP is the market value of the final goods and services produced locally over a period — the key word is final: the value of intermediate inputs is already inside the final product. For example, a loaf sells for $9, a value that already includes the wheat and the flour; adding all three together would double-count and overstate the economy.
- Step 2: The production (value-added) approachThe production approach sums the value added of every industry, where value added equals output value minus the cost of intermediate inputs. For example, a farmer grows wheat and sells it for $2 — value added $2; a mill buys the wheat for $2, mills it into flour and sells for $5 — value added $3; a bakery buys the flour for $5, bakes bread and sells for $9 — value added $4. The three stages add to $9, exactly the value of the final product, showing the two methods agree.
- Step 3: The expenditure approachThe expenditure approach sums four kinds of spending: GDP ＝ private consumption expenditure ＋ investment expenditure ＋ government expenditure ＋ exports − imports. For example, a family dining out is private consumption; a firm buying machines and premises is investment; the government building roads and employing civil servants is government expenditure; exports are foreign spending on local goods, while imports are local purchases of foreign goods and must be deducted because they are not locally produced.
- Step 4: The income approachThe income approach sums the factor incomes earned in production: wages, rent, interest and profit. The same total should emerge from the production, expenditure and income angles: what the product sells for is what buyers spend and what producers distribute as income. For example, of the $9 a bakery takes in, after paying for materials, rent and interest, the rest goes to employees as wages and to the owner as profit — income and expenditure mirror each other, measuring one and the same total.
- Step 5: Nominal versus realNominal GDP is valued at current market prices and moves with both output and prices; real GDP is valued at base-period fixed prices, removing price changes and reflecting output alone. Conversion: real ＝ nominal ÷ GDP implicit price deflator × 100. For example, nominal GDP rises from $100 billion to $110 billion, but if prices rose 10 percent over the same period, real output is flat — performance comparisons must always use real figures.
- Step 6: GDP at factor costFigures at market prices include the effects of indirect taxes and subsidies: indirect taxes push prices up while subsidies push them down, and both drive market prices away from what the factors of production actually earn. GDP at factor cost ＝ GDP at market prices − indirect taxes ＋ subsidies. For example, a bottle of water carries $1 of tax in its price; that dollar is no factor income, and only after removing it does the figure reflect what truly accrues to wages, rent, interest and profit.
- Step 7: Per-capita figures and the growth ratePer capita GDP ＝ GDP ÷ population, removing differences in population size for cross-economy comparison of living standards. The growth rate is computed on real figures: growth rate ＝ (this year's real GDP − last year's real GDP) ÷ last year × 100%. For example, real GDP rising from $200 billion to $210 billion is 5 percent growth — the basic gauge of expansion or contraction and the basis for government and business decisions.
5Worked example Example
Application: an economy's national income statistics for a year are (in billion dollars): private consumption expenditure 100; investment expenditure 30; government expenditure 25; exports 40; imports 35. The population is 5 million. (a) Compute GDP by the expenditure approach. (b) Compute per capita GDP. (c) If next year nominal GDP is 176 billion and the GDP implicit price deflator is 110 (base year ＝ 100), has real GDP grown?
- State the expenditure formula: GDP ＝ private consumption ＋ investment ＋ government expenditure ＋ exports − imports
- Substitute: 100 ＋ 30 ＋ 25 ＋ 40 − 35 ＝ 160 billion dollars
- Per capita: 160 billion ÷ 5 million ＝ $32,000
- Convert to real terms: next year's real GDP ＝ 176 ÷ 110 × 100 ＝ 160 billion, the same as this year
- Judgement: the entire nominal rise of 16 billion came from price increases — real GDP did not grow
- Answer: (a) GDP ＝ 100 ＋ 30 ＋ 25 ＋ 40 − 35 ＝ 160 billion dollars. (b) Per capita GDP ＝ 160 billion ÷ 5 million ＝ $32,000. (c) Next year's real GDP ＝ 176 ÷ 110 × 100 ＝ 160 billion, unchanged from this year, so there is no real growth; the nominal rise of 16 billion came entirely from price increases. Measuring performance must rest on real figures — nominal figures are misled by inflation.
6Common mistakes Mistakes
7Quick check Quick check
Q1Why does GDP count only final goods and services?
Q2Private consumption is $80 billion, investment $20 billion, government expenditure $15 billion, exports $30 billion, imports $26 billion. What is GDP?
Q3What is the difference between nominal and real GDP?
Q4Nominal GDP is $132 billion and the deflator is 120 (base year ＝ 100). What is real GDP?
Q5Why should living-standard comparisons use real per-capita GDP?
8Recap Recap
- National income is the collective name for aggregates such as GDP and gross national income
- GDP can be computed from the production (value-added), expenditure and income approaches — conceptually the same total
- Expenditure approach: private consumption ＋ investment ＋ government expenditure ＋ exports − imports
- Nominal figures use current prices, real figures remove price changes; performance comparisons must use real figures
- Factor-cost valuation removes indirect taxes and subsidies; real per-capita figures aid cross-economy comparison