National income refers to the total value of all goods and services produced within a country’s borders during a specific time period. It serves as a crucial indicator of a country’s economic performance and standard of living. Various concepts and methods are used to measure national income. Here are the key concepts and measurement methods:

1. Gross Domestic Product (GDP): GDP is the most commonly used measure of national income. It represents the total value of all final goods and services produced within a country’s borders in a specific time period, typically a year. GDP can be calculated using three approaches:a. Production Approach: This approach adds up the value added at each stage of production across all industries. It calculates GDP as the sum of value-added contributions by firms.

   b. Income Approach: This approach calculates GDP by summing up all the incomes earned in the economy, including wages, rents, interest, and profits.

   c. Expenditure Approach: This approach calculates GDP by summing up all the spending on final goods and services in the economy. It includes consumption, investment, government spending, and net exports (exports minus imports).

2. Gross National Product (GNP): GNP measures the total value of all goods and services produced by a country’s residents, whether within the country or abroad. It includes income earned by citizens and companies outside the country and excludes income earned by foreigners within the country.
3. Net National Product (NNP): NNP is derived by subtracting depreciation (wear and tear) from GNP. It represents the net value of goods and services produced after accounting for the capital used up in the production process.
4. National Income: National income is the income earned by individuals and businesses in the production of goods and services. It is derived by subtracting indirect taxes (taxes on products and services) and adding subsidies from NNP.
5. Personal Income: Personal income refers to the income received by individuals from all sources, including wages, salaries, rent, interest, dividends, and transfer payments like social security benefits and welfare payments.
6. Disposable Income: Disposable income is the income available to individuals after paying taxes to the government. It represents the income that can be consumed or saved.

Methods of Measurement:

1. Output/Production Method: This method calculates national income by summing up the value-added contributions of all sectors in the economy. It measures the output at each stage of production and avoids double-counting by considering only the value added at each stage.
2. Income Method: This method calculates national income by summing up the incomes earned by individuals and businesses involved in the production process. It includes wages, salaries, rents, interest, and profits.
3. Expenditure Method: This method calculates national income by summing up the total expenditure on final goods and services in the economy. It includes consumption expenditure, investment, government spending, and net exports.
4. Value-Added Method: This method focuses on calculating the value added at each stage of production across all industries. It avoids double-counting by considering only the value added by each industry.

These methods of measurement are interrelated, and they should provide similar results when applied correctly. National income accounts are typically compiled by national statistical agencies using a combination of data sources, including surveys, administrative records, and official economic reports, to estimate the various components of national income.