Price elasticity of supply

Elastic supply is when the quantity supplied changes by a larger percentage than the price (1), so PES is greater than 1; producers can respond strongly to a price change (e.g. a manufactured good with spare capacity) (1).

PES = % change in quantity supplied ÷ % change in price (1) = +5% ÷ +25% = +0.2 (1). Since PES = 0.2, which is between 0 and 1, supply is inelastic (1) — quantity supplied responds less than proportionately to the price change, as expected for a perishable good like milk that cannot be stored or quickly increased (1).

Supply is price-elastic when quantity supplied responds strongly to a price change, and a manufactured good with spare capacity fits this well. Spare capacity means the firm has idle machines and available workers that are not currently being used. So when the price rises and supplying becomes more profitable, the firm can quickly bring these unused resources into production and raise output substantially, without waiting to build new factories — quantity supplied rises a lot, so supply is elastic. Manufactured goods are also typically non-perishable, so the firm can hold and release stocks, adding to its ability to respond quickly. In addition, the inputs (raw materials, labour) for manufacturing are often readily available, so production can be scaled up at short notice. By contrast, a firm at full capacity could not respond this way, so its supply would be inelastic. So spare capacity makes supply elastic because the firm can increase output rapidly when the price rises.

When supply is inelastic, quantity supplied responds very little to a price change, so the supply curve is steep. If demand increases (the demand curve shifts right), there is a shortage at the original price, which bids the price up. Because supply is inelastic, producers cannot raise output much in response, so the extra demand is met mainly by a large rise in price rather than a rise in quantity — the new equilibrium shows a big increase in price and only a small increase in quantity. The more inelastic the supply, the larger the price rise for any given increase in demand. This is exactly why markets with inelastic supply — such as agriculture, housing or event tickets — show such volatile prices: when demand jumps, prices spike because output cannot expand quickly. So inelastic supply means that changes in demand fall mostly on price, not quantity.

Inelastic agricultural supply causes volatile prices and unstable incomes for farmers, so there is a case for help, though intervention has costs. Why a government should intervene: because supply cannot respond to price, a good harvest can make prices collapse and a poor harvest make them spike, so farmers' incomes are very unstable, making it hard for them to plan or invest; farming may also be vital for food security and rural employment. The government could use buffer stocks (buying and storing when prices are low, releasing when high) to stabilise prices, set guaranteed minimum prices, or pay subsidies to support incomes. Why it might not, or should be careful: intervention is expensive (storage costs, the opportunity cost of the money), buffer stocks can be mismanaged, minimum prices create surpluses that must be bought up, and support can make farmers inefficient or dependent; consumers may also pay higher prices. Judgement: there is a strong case for some intervention because price and income instability from inelastic supply is a genuine problem that the market does not solve on its own, and food/rural livelihoods matter. But the help should be well-designed and limited — a buffer stock to smooth prices is often better than permanent high minimum prices, which create waste and dependency. So whether to intervene depends on the cost, the design of the scheme, and how serious the instability is.

The ability to store a good affects its PES, but whether it is the most important factor is debatable. Why storability matters a lot: if a good can be stored (e.g. manufactured goods or grain held in inventory), producers can release stock quickly when the price rises, so quantity supplied responds strongly — supply is elastic; if a good is perishable (fresh milk, fish, flowers) it cannot be stored, so supply is inelastic. So storability clearly influences how fast supply can respond. Why other factors may matter more: the time period is often the strongest factor — in the short run almost any good has inelastic supply because output cannot be expanded, while in the long run firms can build capacity; spare capacity determines whether a firm can raise output at all when price rises; and factor mobility (how easily resources switch into the good) also matters. For a non-storable service, spare capacity and time dominate, not storage. Judgement: storability is one important factor — decisive in distinguishing perishable from storable goods — but it is not always the most important; the time period is usually the most fundamental influence on PES, with spare capacity also crucial. So the most important factor depends on the good: for perishables, storability is key, but for most goods time and capacity matter more. Therefore storability is significant but not universally the most important.