Which economic sector is not determined by measuring specific sources of income?

The net foreign sector is focused on the transactions between one country's economy and the rest of the world, particularly concerning exports and imports. Instead of being directly tied to measurable income sources like wages or profits, it encompasses overall trade balances—essentially measuring the economic interactions but not defined by individual income streams within a country.

In contrast, the other sectors—household, public, and business—rely on specific sources of income. Households derive income from wages and investments; the government sector's income comes from taxes and government revenue; and businesses generate income through sales and investments. Therefore, the net foreign sector stands apart because it looks at broad economic relationships rather than specific sources of income, thus making it unique among the options provided.