Stocks and flows

A specified date identifies a point in time. A variable measured at one point, such as wealth, population, money balances, or capital assets on that date, is generally a stock. A flow instead records an amount accumulated or occurring over an interval, such as monthly income, annual output, or yearly expenditure. Therefore, the date clue indicates stock.

A stock is a quantity existing or available at a particular point of time, such as wealth, population, or inventory on a date. A flow is a quantity measured over a period, such as income, production, or expenditure during a year. Therefore, option B states the fundamental distinction correctly.

Annual purchases are transactions occurring throughout the year, so their total is measured over a period and is a flow. Goods remaining at the end of the year are an inventory balance measured at one point of time, so they are a stock. Purchases may change the inventory stock, but the two classifications remain different.

The most reliable rule is to examine the time reference. A quantity stated at a point of time, such as wealth on 31 March, is a stock. A quantity measured over a period, such as income during a year, is a flow. Price, ownership, or whether an item is domestic does not determine the classification.

A company's total liabilities stated on 31 March are measured at a specific point of time, so they constitute a stock variable. Liabilities are a balance owed at that date. Annual income and monthly expenditure are flows because they represent amounts earned or spent over periods rather than a balance existing on one date.

Interest paid during the year is a payment made over a specified period, so it is a flow variable. It records the amount of interest paid throughout the year. The outstanding debt or cash balance on a particular date would be a stock, but the interest payment during the year is not a balance.

Total wealth today is measured at a particular point in time, so it is a stock. It represents the household’s accumulated assets, after considering relevant liabilities, on that date. Total income this month is earned and measured over the whole month, so it is a flow. The words today and this month provide the decisive time references.

The decrease in a country’s capital stock is measured over the course of a year, not at one particular instant. Therefore, it is a flow variable. A flow records a change, addition, or movement during a specified period, whereas the capital stock itself is a stock variable measured at a point in time.

An accumulated amount is a balance existing at a particular point of time, so it is treated as a stock. A newly added amount records an addition during a period, so it is a flow. For example, accumulated savings are a stock, while savings made during a month are a flow. Hence option B is correct.

Government debt outstanding on a particular date is a stock because it is measured at a point in time. Interest paid during the year is a flow because it represents a payment accumulated over a period. Thus, the correct classification is stock and flow, given in option C.

Wealth is the total value of assets owned at a particular point in time, so it is a stock variable. Saving is the part of income not consumed during a period and is measured over a month, year, or another interval, so it is a flow variable. Therefore, option B is correct.

Foreign exchange reserves reported on a particular day show the amount held at that point in time, so they are a stock variable. Export earnings received over one year are measured across a period and therefore are a flow variable. The correct sequence is stock and flow, given in option D.

National income is the income generated or received during a specified period, usually a year, so it is a flow variable. National wealth is the total value of assets owned by a nation at a particular point in time, so it is a stock variable. Hence, option B is correct.

A shop’s sales for a month are measured by the transactions completed throughout that month, so sales are a flow variable. The inventory of goods at the end of the month is measured on a particular date or point in time, so it is a stock variable. Therefore, the correct order is flow and stock, or option C.

The phrase “increased during the year” refers to a change occurring over a defined period. Such an addition to capital is measured as investment during the year and is therefore a flow variable. The capital stock at the beginning or end of the year would instead be a stock. Hence option D is correct.

A flow variable is measured over a specified period, such as income earned during a year, expenditure during a month, or output produced in a quarter. It records an activity or change occurring through time. In contrast, a stock variable is measured at a particular point in time. Hence, option B is correct.

Saving is a flow when it is measured as the amount accumulated during a specified period, such as one year. Options A, B, and D describe balances or asset values at a point in time, which are stock concepts. Therefore, the amount saved during one year, option C, is the correct answer.

A stock variable measures the amount of something existing at a particular point in time or on a specified date, such as wealth, cash balance, debt, or capital stock. Options B, C, and D describe quantities accumulated or produced over periods, so they are flow variables. Thus, option A is correct.

The number of tractors owned today is measured at a particular point in time and is therefore a capital stock. The number of tractors bought during the year is measured over a period and represents an investment flow. Hence the correct order is stock and flow, option B.

The student's pocket-money balance today is a stock because it is measured at a specific point in time, namely today. Pocket money received during the month is a flow because it records an amount over a period of time. A stock is an accumulated quantity existing at a date, whereas a flow measures an activity or transaction occurring during an interval. Therefore, the correct order is stock and flow, option B.

Tax revenue received during a year is a flow because it is measured over a definite period, the entire year. Government debt outstanding at the end of the year is a stock because it is measured at a particular point in time and represents the accumulated unpaid liability existing then. The fact that debt may have resulted from earlier borrowing does not make the outstanding balance a flow. Thus, the correct order is flow and stock, option C.

A company's cash balance at the end of the day is a stock because it states how much cash exists at a particular point in time, the day's end. Total cash receipts during that day are a flow because they measure money received over the whole daily interval. The balance is an accumulated amount at a date, while receipts are transactions occurring during a period. Therefore, option A is correct.

A stock is measured at a particular point of time, whereas a flow is measured over a period. The existing stock of machines represents the firm’s capital available at a point in time. Machines purchased during the year represent investment occurring throughout that year and therefore add to the stock. Hence, option A correctly pairs a stock with its related flow.

The governing concept is that a stock is measured at a date, whereas a flow is measured over a time interval. A household’s total liability today means the outstanding amount owed at this particular date; it is therefore a stock. The new loan taken during the month refers to borrowing that occurs throughout a defined period and is measured as an addition during that period; it is therefore a flow. The correct sequence is stock followed by flow, which is stated in option D. Option A reverses both classifications, option B wrongly treats the month’s borrowing as a point-in-time amount, and option C reverses the order. The words “today” and “during the month” provide the decisive clues.

Wealth is the value of assets owned at a particular point in time, so it is a stock. Income is earned through wages, rent, interest, or profit during a period such as a month or year, so it is a flow. Therefore, option C correctly distinguishes the two concepts.