Elasticity Masterclass: PED, PES, YED & XED Explained
- Excel in Economics
- Jun 29
- 3 min read
Updated: Jul 12
Elasticity is the beating heart of Microeconomics. If you don't fully grasp how consumers and producers respond to changes in price, income, or related goods, you will struggle with almost every other topic in the syllabus (especially Government Intervention and Theory of the Firm).
In this masterclass, we will cover the four core elasticities: PED, PES, YED, and XED, and how to use them to score top marks.
1. Price Elasticity of Demand (PED)
Definition: PED measures the responsiveness of the quantity demanded of a good to a change in its price.
Formula: `%Δ Quantity Demanded / %Δ Price`
The Core Concept: If a good is price inelastic (PED < 1), consumers are not very responsive to price changes. This usually applies to necessities (water, electricity) or addictive goods (cigarettes). If a good is price elastic (PED > 1), consumers are highly responsive to price changes (e.g., luxury holidays or goods with many substitutes).
Why it matters for exams: Governments must know the PED before setting indirect taxes. Taxing an inelastic good (like tobacco) raises massive tax revenue but doesn't reduce consumption much. Taxing an elastic good severely reduces consumption but raises little revenue.
[ 🖼️ INSERT PED DIAGRAM HERE ]
2. Price Elasticity of Supply (PES)
Definition: PES measures the responsiveness of the quantity supplied of a good to a change in its price.
Formula: `%Δ Quantity Supplied / %Δ Price`
The Core Concept: PES is all about time and flexibility. In the short run, supply is almost always inelastic (PES < 1) because a firm cannot instantly build a new factory or grow crops faster just because the price went up. In the long run, supply becomes more elastic as firms can expand capacity.
Why it matters for exams: Primary commodities (agriculture, mining) have highly inelastic PES compared to manufactured goods. This explains why commodity prices are incredibly volatile in global markets when demand shifts.
3. Income Elasticity of Demand (YED)
Definition: YED measures the responsiveness of demand to a change in consumer income.
Formula: `%Δ Quantity Demanded / %Δ Income`
The Core Concept: YED tells us what *type* of good we are looking at. - Normal Goods (YED > 0): As income rises, demand rises (e.g., restaurant meals). - Inferior Goods (YED < 0): As income rises, demand falls (e.g., cheap instant noodles, public transport). Consumers switch to better alternatives.
Why it matters for exams: During a recession (falling incomes), firms selling inferior goods will actually see a boom in sales, while firms selling luxury normal goods (YED > 1) will suffer massively.
4. Cross Elasticity of Demand (XED)
Definition: XED measures the responsiveness of demand for Good A following a change in the price of Good B.
Formula: `%Δ Quantity Demanded of Good A / %Δ Price of Good B`
The Core Concept: - Substitutes (XED > 0): If the price of Pepsi goes up, the demand for Coke goes up. - Complements (XED < 0): If the price of printers goes up, the demand for ink cartridges goes down.
Why it matters for exams: Firms use XED for pricing strategies. A company might sell a video game console at a loss (reducing the price) because they know the XED is highly negative for games, meaning they will make massive profits on the complementary software.
The Ultimate Exam Tip
Never write an essay about a microeconomic policy without mentioning elasticity. Whether it is a tax, a subsidy, a minimum wage, or a trade tariff, the final outcome always depends on the elasticities of the relevant curves. Using this as your final evaluation point is a guaranteed way to hit Level 5 on the mark scheme!
