When a variable is associated with time period, it is_____________

Analyze the question: The question asks what we call an economic variable that is measured over a period of time (e.g., per day, per month, per year).

Explain the concept: Economists classify variables into two types:

• Stock variable: measured at a particular point in time. Examples: money supply on 31st December, the amount in your bank account today, the number of unemployed people on a given date.
• Flow variable: measured over a period of time. Examples: income per month, national output per year, expenditure per week, the interest earned in a year.

Solution, step by step:

1. The question says the variable is "associated with a time period" (per day, per month, per year).
2. A variable tied to a time period is measured as a rate over that period, which is the definition of a flow.
3. Checking the other options: • Circular: relates to the circular flow of income, not a type of variable. • Static: means unchanging or fixed at a point, so it does not fit a variable measured over time. • Stock: is tied to a point in time, not a period.

Answer: Option B, a flow.

Tip: Think of a river (flow) and a lake (stock). A river is measured as water passing per hour or per day, while a lake is measured as the amount of water at this moment. If you see "per month," "per year," or "over a period," think flow. If you see "as at" a date, think stock.