AP Syllabus focus: ‘A firm's demand for a resource depends on productivity, the output price, and the factor's cost.’
Resource (factor) demand explains how many workers, machines, or acres a firm is willing to hire at different factor prices. It is driven by how much extra revenue each additional unit of the resource generates.
Resource demand as a derived demand
Resource demand is derived from product demand: firms hire inputs because inputs help produce output that consumers buy. If consumers value the output more, the resource becomes more valuable to the firm.
The firm’s willingness to pay for an additional unit of a resource is tied to the additional revenue that unit creates.
Marginal revenue product (MRP): The additional revenue a firm earns from employing one more unit of a resource, holding other inputs constant.
In most AP graphs, a firm’s resource demand curve is its MRP curve: at each possible quantity of the input, MRP indicates the maximum the firm would be willing to pay for that unit (because paying more would reduce profit).
= Extra output produced by one more unit of the resource (units of output)
= Extra revenue from selling one more unit of output (dollars per unit of output)
This figure illustrates the firm’s marginal revenue product schedule as a downward-sloping curve and explicitly labels the relationship . It helps connect the algebra in the notes to the graphical interpretation of factor demand: each point on the curve represents the additional revenue generated by the next unit of labor. Source
Because marginal product typically diminishes as more of a variable input is used with fixed inputs, MRP often slopes downward, helping explain the downward-sloping shape of resource demand.
What determines resource demand?
1) Productivity of the resource (how much it can produce)
Productivity affects resource demand through MP (how much extra output the input creates). If workers or machines become more productive, each additional unit tends to add more output and therefore more revenue.
Common productivity influences include:
Improvements in technology or production processes
Better training, health, or task specialisation
More or higher-quality complementary inputs (e.g., better software raising office-worker MP)
When productivity rises:
MRP increases at each quantity of the resource
The resource demand (MRP) curve shifts right
Firms become willing to hire more of the resource at any given factor price
2) Output price (the price the firm receives for what the resource helps produce)
A resource is more valuable when the firm can sell the resulting output at a higher price. A higher output price raises the revenue generated by each unit of extra output, which increases the resource’s MRP.
Mechanism:
Higher output price generally increases MR (or raises revenue per unit sold)
With MP unchanged, higher MR implies higher MRP
The resource demand (MRP) curve shifts right
Conversely, if the output price falls (often due to weaker consumer demand), the resource demand curve shifts left because the same physical contribution by the input now generates less revenue.
3) The factor’s cost (the price of the resource)
A firm’s quantity of the resource demanded depends on the resource’s own price (for labour, the wage; for capital, the rental rate). Holding MRP constant, a higher factor price makes each unit of the resource less profitable.
Key implication:
A change in the factor’s cost causes a movement along the resource demand (MRP) curve, not a shift of that curve
Higher factor price → lower quantity of the resource demanded
Lower factor price → higher quantity of the resource demanded
It is useful to separate:
Shifters of resource demand (MRP): productivity and output price
Movements along resource demand: changes in the factor’s cost
Interpreting “depends on” in AP terms
For AP Microeconomics, “a firm’s demand for a resource” is best interpreted as the firm’s willingness to hire different quantities at different factor prices, based on:
How much additional output the resource creates (productivity)
How much revenue per unit of output the firm can earn (output price)
How much the resource costs per unit (factor price)
FAQ
If an input becomes cheaper and is a substitute for labour (e.g., automation), firms may use more capital and demand less labour.
If an input is a complement (e.g., better tools), cheaper or higher-quality complements can raise labour productivity, increasing labour demand.
In the long run, firms can adjust plant size, adopt new technology, and reorganise production.
That flexibility makes it easier to substitute away from relatively expensive inputs, increasing the responsiveness of resource demand to input-price changes.
$MRP$ uses marginal revenue: $MRP = MP \times MR$.
“Value of marginal product” uses output price: $VMP = MP \times P$. They coincide only when the firm’s $MR = P$ (typically under perfect competition in the output market).
Stronger consumer demand tends to raise output price and/or increase the quantity the firm can sell at a given price.
Either effect can increase the revenue attributable to extra output, raising $MRP$ and shifting labour demand right.
Usually, the resource’s own cost changes the quantity demanded along the existing $MRP$ curve.
However, if a cost change also alters productivity (e.g., higher wages attract higher-quality applicants, raising $MP$), then $MRP$ may change and the demand curve can shift as well.
Practice Questions
Question 1 (3 marks) Explain how an increase in worker productivity affects a firm’s demand for labour.
States that higher productivity increases the marginal product of labour (1)
Links higher marginal product to higher marginal revenue product, (1)
Concludes that the firm’s labour demand (MRP) curve shifts right / labour demanded increases at any given wage (1)
Question 2 (6 marks) A firm experiences (i) an increase in the market price of its output and (ii) an increase in the hourly wage it must pay. Explain the effect of each change on the firm’s demand for labour, clearly distinguishing between a shift of labour demand and a movement along it.
Identifies labour demand as derived from (1)
Explains that a higher output price raises revenue generated by each worker, increasing (1)
States that labour demand shifts right when rises (1)
Explains that a higher wage increases the cost of labour (1)
States that a wage increase causes a movement along the labour demand curve to a lower quantity of labour demanded (1)
Clearly distinguishes shift (from output price change) vs movement along (from wage change) (1)
