Stocks and flows

Loan outstanding at the beginning of the year is the accumulated balance existing at a particular date, so it is a stock. New loans disbursed during the year are transactions made over a time interval, so they are a flow. The amount disbursed may later add to the outstanding stock, but the disbursement itself remains a flow.

National wealth is the accumulated value of assets held by a country at a particular point in time, so it is a stock. GDP measures the value of final goods and services produced within the country during a specified period, generally one year, so it is a flow. Therefore C gives the correct distinction.

The number of machines owned on a specified date is a quantity existing at one point in time, so it is a capital stock. The annual value of wear and tear, called depreciation, is measured over the year, so it is a flow. Therefore the correct classification is stock followed by flow.

Saving during the year is measured over a period, so it is a flow. The total amount accumulated in the bank by the end of the year is a balance measured at a particular date, so it is a stock. The flow of saving can add to the stock of wealth, but the two measurements must not be confused.

Profit is the excess of revenue over cost earned during a specified accounting period, so profit for that period is a flow. Total assets are valued on a particular balance-sheet date and represent an accumulated position, so they are a stock. The time reference, not the monetary form, determines the classification.

A firm's output during the year represents the quantity produced over an entire period, so it is a flow. Finished-goods stock at the end of the year represents the inventory available at one specific point in time, so it is a stock. The words “during the year” indicate a flow, whereas “at the end of the year” indicates a stock. Therefore, the correct sequence is flow and stock.

Births and deaths counted during one year are events occurring over a time interval. Their annual numbers therefore represent flows, just like annual production or expenditure. They are not stocks because neither measure describes the total number existing at one particular date. Hence both births and deaths are flows.

Population on a specified date is the total number existing at one point in time, so it is a stock. Population increase during the year is the change occurring over a time interval, so it is a flow. The increase may result from births, deaths, and migration, but its annual measurement remains a flow.

Foreign exchange reserves stated on a particular date are the accumulated amount of foreign assets available at that point, so they are a stock. Calling them a flow is incorrect. Annual income, investment, and monthly expenditure are normally measured over periods and are therefore flows. Hence C is the mistaken statement.

Exports recorded during one year are measured over a period of time, so they are a flow, not a stock. The statement in option B incorrectly labels them as a stock. In contrast, total debt on a specified date, capital stock on a specified date, and a bank balance at the end of a day are measured at particular points in time and are therefore stocks. Thus, B is the incorrect classification.

Raw material used during the month is measured over the entire month, so it is a flow. Raw material stock at the end of the month is the quantity remaining at a particular point in time, so it is a stock. The same physical material can therefore appear as a flow when used and a stock when held at a date.

The question asks for an annual flow first and a year-end stock second. Annual depreciation is the loss of value measured over a year, so it is a flow. Capital stock at year end is the accumulated quantity existing on a particular date, so it is a stock. Therefore A has the required order.

Year-end government debt is the accumulated liability outstanding at a specific date, so it is a stock. Annual interest payment is measured over the whole year, so it is a flow. Option A has the reverse order, while C and D contain two period measures. Thus B is the only correct year-end-stock followed by annual-flow pair.

Capital stock represents the quantity of capital existing at a particular point in time, such as the value of machinery on 31 March. Investment records additions made during a period, such as a year. Therefore capital stock is a stock and investment is a flow; option A gives both the classification and the correct reason.

Inventory at any particular date is a stock, but the change in inventory is measured by comparing two dates over an accounting period. If closing inventory exceeds opening inventory, the difference is positive. This positive change is treated as a flow during the period and may be included as inventory investment. Therefore, option A is correct.

Inventory held at any particular date is a stock. However, the difference between closing and opening inventory measures what happened during the period. When closing inventory is smaller, the change is negative, so it is correctly described as a negative flow, not a negative stock.

Opening inventory and closing inventory are both stock levels measured at particular dates. Their difference, however, indicates the increase or decrease in inventory over the accounting period. That change is a flow measure. The other options already describe activities occurring over periods.

Public debt is the outstanding liability accumulated up to a particular date, so it is a stock. Annual tax revenue is the amount collected throughout a financial year, so it is a flow. The same time distinction applies to borrowing and expenditure, but option B gives the requested correct pair.

Capital stock is the amount of productive capital existing at a point in time. Net investment is the period-wise addition to capital after allowing for depreciation. When net investment is positive, additions exceed depreciation and the capital stock rises. The other options are stock measures, not the relevant flow.

A stock is a quantity measured at a particular point in time, such as wealth, debt, or inventory on a date. A flow is measured over a period, such as income, saving, or investment. Flows can add to or subtract from a stock, causing its level to change between two dates. Thus, option C expresses the relationship most precisely.

Capital available today states the amount of capital existing at a particular point in time, so it describes a stock level. Investment during a year, depreciation during a year, and saving during a month are all flows measured over periods; each can change the capital stock. Therefore, option B is the only stock-level example.

Capital stock is measured at a point in time, whereas depreciation is a flow occurring over a period. Wear and tear on machines reduces the existing capital stock, so annual depreciation represents erosion of a stock by a flow. Investment, saving, and births instead increase stocks.

New investment is expenditure on additions to productive assets during a period, so it is a flow. Those additions increase the economy’s or firm’s capital stock, which is measured at a point in time. Debt repayment, deaths, and depreciation are also flows, but they reduce the associated stock rather than expand it. Hence, option D is correct.

Borrowing is a flow that adds to the public debt stock, while repayment is a flow that subtracts from it. If repayment exceeds new borrowing, and other adjustments are ignored, the outstanding debt stock will fall. Thus option A is the only economically valid conclusion; the stock does not become a flow.

A flow is measured over an interval, such as national income during a year, and therefore is often expressed as an amount per period or rate. A stock is measured at a point in time, such as capital on 31 March, and represents a level. Option A states both definitions correctly.