Producer Behaviour and Supply

The One Thing

Producer behaviour concerns how firms combine inputs, evaluate costs and revenues, select a profit-maximising output level, and respond to price and other market changes through supply. The central equilibrium condition is MR = MC, provided that marginal cost is rising at the equilibrium output.

Who and What

• Production: The process of transforming inputs into goods and services.
• Factors of production: The inputs used in production: land, labour, capital and entrepreneurship.
• Production function: The technical relationship between inputs and the maximum possible output: Q = f(L, K), where Q is output, L is labour and K is capital.
• Short run: A period in which at least one factor of production is fixed, while other factors can be varied.
• Long run: A period long enough for all factors of production to be changed.
• Total product (TP): The total quantity of output produced with given inputs.
• Average product (AP): Output per unit of a variable input: AP = TP ÷ units of the variable input.
• Marginal product (MP): The change in total product resulting from one additional unit of a variable input: MP = change in TP ÷ change in input.
• Law of variable proportions: As additional units of a variable input are combined with fixed inputs, marginal product may first rise, then fall, and eventually become negative.
• Returns to a factor: The change in output resulting from increasing one variable input while other inputs remain fixed.
• Fixed cost (TFC): A cost that does not vary with output in the short run, such as rent or a fixed licence fee.
• Variable cost (TVC): A cost that changes with output, such as expenditure on raw materials.
• Total cost (TC): The sum of fixed and variable costs: TC = TFC + TVC.
• Average fixed cost (AFC): Fixed cost per unit: AFC = TFC ÷ Q. AFC falls continuously as output increases, assuming fixed cost remains constant.
• Average variable cost (AVC): Variable cost per unit: AVC = TVC ÷ Q.
• Average cost (AC): Total cost per unit: AC = TC ÷ Q = AFC + AVC.
• Marginal cost (MC): The change in total cost caused by producing one additional unit: MC = change in TC ÷ change in Q. Since fixed cost does not change with output, MC is also the change in TVC divided by the change in Q.
• Total revenue (TR): The total money received from sales: TR = P × Q.
• Average revenue (AR): Revenue per unit: AR = TR ÷ Q. Under perfect competition, AR equals price.
• Marginal revenue (MR): The change in total revenue resulting from selling one additional unit: MR = change in TR ÷ change in Q.
• Producer equilibrium: The output level at which profit is maximised or loss is minimised, so the producer has no reason to alter output.
• Profit: The difference between total revenue and total cost: Profit = TR − TC, or Profit = (AR − AC) × Q.
• Perfect competition: A market with many buyers and sellers, homogeneous products, free entry and exit, and firms that accept the market price. Under perfect competition, P = AR = MR.
• Supply: The quantity of a commodity a producer is willing and able to sell at different prices during a specified period.
• Supply schedule: A table showing quantities supplied at different prices.
• Supply curve: A graph showing the relationship between price and quantity supplied.
• Law of supply: Other things remaining constant, quantity supplied generally increases when price rises and decreases when price falls.
• Change in quantity supplied: Movement along the same supply curve caused solely by a change in the commodity’s own price.
• Change in supply: A shift of the entire supply curve caused by factors other than the commodity’s own price.
• Elasticity of supply: The responsiveness of quantity supplied to a change in price: Es = percentage change in quantity supplied ÷ percentage change in price.
• Perfectly inelastic supply: Quantity supplied does not change when price changes; Es = 0.
• Unitary elastic supply: Quantity supplied changes in the same proportion as price; Es = 1.
• Perfectly elastic supply: An extremely small change in price causes an unlimited change in quantity supplied; Es = ∞.

Causes and Consequences

• A producer combines land, labour, capital and entrepreneurship to transform inputs into goods and services. The production function expresses this technical relationship as Q = f(L, K), where output depends on labour and capital when other relevant conditions are given.

• In the short run, at least one factor is fixed. Increasing a variable input while fixed inputs remain unchanged produces returns to a factor governed by the law of variable proportions: marginal product may initially rise, then fall, and eventually become negative.

• The relationships between TP, AP and MP determine production outcomes:

- When MP > AP, AP rises. - When MP = AP, AP is at its maximum. - When MP < AP, AP falls. - When MP is positive, TP rises. - When MP = 0, TP is at its maximum. - When MP is negative, TP falls.

• Production creates costs. Total cost is given by TC = TFC + TVC. Fixed costs, such as rent or a fixed licence fee, remain unchanged with output in the short run, whereas variable costs, such as raw-material expenditure, change with output.

• Average and marginal costs guide output decisions. AFC = TFC ÷ Q, AVC = TVC ÷ Q, and AC = TC ÷ Q = AFC + AVC. Because fixed cost is constant, average fixed cost falls continuously as output increases. Marginal cost equals the change in total cost divided by the change in output and also equals the change in variable cost divided by the change in output.

• Sales generate revenue. TR = P × Q, AR = TR ÷ Q, and MR = change in TR ÷ change in Q. Under perfect competition, price equals both average revenue and marginal revenue, so P = AR = MR.

• A rational producer expands output while marginal revenue exceeds marginal cost because each additional unit adds more to revenue than to cost. Equilibrium is reached where MR = MC, provided that MC is rising or cuts MR from below. Equality alone is insufficient if MC is falling.

• Profit is calculated as Profit = TR − TC, or Profit = (AR − AC) × Q. A producer earns profit when TR > TC, breaks even when TR = TC, and incurs a loss when TR < TC.

• Under perfect competition, the equilibrium condition becomes P = MR = MC, with MC rising. A firm’s short-run supply curve is the rising portion of its MC curve above the minimum point of AVC.

• The law of supply establishes a direct relationship between price and quantity supplied when other factors remain unchanged. A change in the commodity’s own price causes a movement along the same supply curve, whereas changes in other determinants cause the entire supply curve to shift.

• An increase in input prices, higher taxes or unfavourable production conditions generally decreases supply and shifts the supply curve leftward. Improved technology, lower input prices, subsidies or an increase in the number of firms generally increases supply and shifts the supply curve rightward.

• Other determinants of supply include prices of related goods, producers’ expectations and natural conditions, in addition to the commodity’s own price, input prices, technology, taxes and subsidies, and the number of firms.

• Elasticity of supply is measured by Es = percentage change in quantity supplied ÷ percentage change in price. Using the proportionate method:

Es = (change in Q ÷ Q) ÷ (change in P ÷ P)

Supply is elastic when Es > 1, inelastic when Es < 1, and unitary elastic when Es = 1.

• Supply tends to be more elastic when producers have spare capacity, inputs can be obtained easily, and the time period is longer. It is often less elastic in the immediate period because producers cannot quickly change production capacity.

• The responsiveness of supply also depends on technology, production capacity, the availability of inputs, the time available for adjustment and the ability to store goods.

What Gets Asked

• Explain how the law of variable proportions affects TP, AP and MP, including the conditions under which each measure rises, reaches a maximum or falls.
• Distinguish between fixed, variable, total, average and marginal costs, and apply TC = TFC + TVC, AC = AFC + AVC and MC = change in TC ÷ change in Q.
• Explain producer equilibrium using the marginal approach, including why MR = MC is sufficient only when MC is rising or cuts MR from below.
• Compare profit, break-even and loss outcomes using Profit = TR − TC and Profit = (AR − AC) × Q.
• Distinguish between a movement along a supply curve caused by a change in the good’s own price and a shift in supply caused by input prices, technology, taxes, subsidies, the number of firms, expectations or natural conditions.
• Explain and calculate elasticity of supply, including perfectly inelastic supply, unitary elastic supply, perfectly elastic supply, and the effects of time, spare capacity, input availability, technology and storage.