Elasticities Notes: PED, PES, YED, XED for A-Level & IB Economics

Curated by Kelvin Hong, founder of The Economics Tutor. Part of our Free Economics Notes series.

Start here — Mr Kelvin Hong sets out both elasticity measures, their formulas and their determinants before we apply them.

Covers the mathematical formulas for PED and PES, what makes demand or supply responsive, and how each looks on a diagram. Everything further down this page — tax incidence, the total revenue rule, pricing strategy — builds on these foundations.

Elasticity is a fundamental concept in economics that measures the responsiveness of one economic variable to a change in another. When applied to demand and supply, it helps us quantify the magnitude of consumer and producer reactions to changes in price, income, or related goods’ prices.

Elasticity is not just a formula; it is the “Diagnostic Tool” of Economics. Whether you are analysing the impact of a Carbon Tax on producers vs consumers (Tax Incidence) or predicting how a Grab fare hike affects demand for MRT rides (XED), this chapter is crucial for Case Studies (CSQ) and Essays.

What you will learn:

• Price Elasticity (PED): The Total Revenue Rule & Pricing Strategies.
• Income Elasticity (YED): Normal vs Inferior Goods (and Singapore’s Luxury Cars).
• Cross Elasticity (XED): Substitutes, Complements & Competitive Strategy.
• Applications: Who pays the tax? (Consumer vs Producer Burden).

⚠️ Note: These are summarised revision notes. To master the specific diagrammatic analysis and evaluation techniques required for the A-Level/IB exams, join our JC Economics Tuition (A-Level) or IB Economics Tuition classes.

Elasticity measures how far you move along a curve — so if the movement-versus-shift distinction is still shaky, start here.

A short refresher on quantity demanded versus demand before applying elasticity to the same curves.

1. Price Elasticity of Demand (PED)

1.1 Definition of PED

Price Elasticity of Demand (PED) measures the degree to which the quantity demanded of a good or service responds to a percentage change in its own price, assuming all other factors remain constant (ceteris paribus). It quantifies how sensitive consumers are to price fluctuations.

1.2 Formula

PED=% Change in Price/% Change in Quantity Demanded

Note: The negative sign is conventionally ignored, and the absolute value is used for interpretation, as per A-Level conventions.

1.3 Interpretation of PED Sign and Value

PED is typically negative because of the inverse relationship between price and quantity demanded (Law of Demand). However, in A-Level economics, we usually interpret the absolute value of PED for simplicity and clarity.

• PED > 1 (Elastic Demand):
  • Interpretation: The percentage change in quantity demanded is greater than the percentage change in price. Consumers are highly responsive to price changes.
  • Graphical Representation: The demand curve is relatively flat.
  • Implications for Firms (Total Revenue):
    • If price decreases, total revenue (TR) increases (due to a proportionally larger increase in quantity demanded).
    • If price increases, total revenue (TR) decreases (due to a proportionally larger decrease in quantity demanded).
  • Example: Luxury goods like designer handbags, expensive restaurant meals, or non-essential foreign holidays. A small price increase for a designer bag might lead to a significant drop in sales as consumers easily opt out or choose cheaper alternatives.
• PED = 1 (Unitary Elastic Demand):
  • Interpretation: The percentage change in quantity demanded is equal to the percentage change in price.
  • Implication for Firms (Total Revenue): Total revenue remains unchanged with a price change.
  • Example: This is often a theoretical benchmark, though some everyday goods might exhibit near-unitary elasticity over a narrow price range.
• PED < 1 (Inelastic Demand):
  • Interpretation: The percentage change in quantity demanded is less than the percentage change in price. Consumers are relatively unresponsive to price changes.
  • Graphical Representation: The demand curve is relatively steep. Implications for Firms (Total Revenue):
    • If price increases, total revenue (TR) increases (due to a proportionally smaller decrease in quantity demanded).
    • If price decreases, total revenue (TR) decreases (due to a proportionally smaller increase in quantity demanded).
  • Example: Necessities like basic foodstuffs (e.g., rice, bread), essential utilities (e.g., electricity, water in the short run), or critical prescription medicine. Even if prices rise significantly, consumers will still purchase these necessities out of need.
• PED = 0 (Perfectly Inelastic Demand):
  • Interpretation: Quantity demanded does not change at all, regardless of any change in price. Consumers are completely unresponsive.
  • Graphical Representation: The demand curve is a vertical line.
  • Example: A life-saving drug for a critically ill patient for whom no substitutes exist. Demand is fixed, regardless of how high the price goes (very rare in its pure form in reality).
• PED = ∞ (Perfectly Elastic Demand):
  • Interpretation: An infinitesimal change in price leads to an infinite change in quantity demanded. Consumers will buy an infinite amount at a specific price, but none at a slightly higher price. This implies extreme price sensitivity.
  • Graphical Representation: The demand curve is a horizontal line.
  • Example: A single firm operating in a perfectly competitive market. If they raise their price even slightly above the market price, they will lose all their customers to competitors selling identical goods. (Highly theoretical in its purest form).

1.4 Determinants of PED

The factors below help explain why the demand for certain goods is more or less elastic:

1. Availability of Close Substitutes:
   • More substitutes = More elastic PED. If consumers can easily switch to alternative goods when the price of a good rises, demand will be more responsive.
   • Fewer substitutes = More inelastic PED. For goods with no close alternatives or for which consumers perceive no good substitutes, demand will be less responsive to price changes.
   • Example: If the price of Coca-Cola rises, many consumers can easily switch to Pepsi, other soft drinks, or even juice, making the demand for Coca-Cola relatively elastic. In contrast, salt has very few readily available substitutes for its primary uses, so its demand tends to remain highly inelastic regardless of price changes.
2. Necessity vs. Luxury:
   • Necessities = More inelastic PED. Goods essential for survival, health, or daily life (e.g., basic food items, medical services, basic utilities) tend to have inelastic demand because consumers need them regardless of price.
   • Luxuries = More elastic PED. Goods that are non-essential, discretionary, or provide pleasure rather than a basic need (e.g., designer clothing, expensive vacations) tend to have elastic demand, as consumers can easily delay or forgo their purchase when prices rise.
   • Example: The demand for insulin for a diabetic patient (a necessity) is highly inelastic, whereas the demand for a high-end sports car (a luxury) is typically very elastic.
3. Proportion of Income Spent on Goods:
   • Large proportion = More elastic PED. If a good represents a significant portion of a consumer’s disposable income, a change in its price will have a noticeable impact on their overall budget and purchasing power, making them more sensitive to price changes.
   • Small proportion = More inelastic PED. For inexpensive items that constitute a tiny or negligible fraction of income (e.g., a single matchbox, a piece of chewing gum), consumers are less likely to react significantly to price changes.
   • Example: A rise in car prices significantly affects demand due to the high cost of cars relative to most people’s income (elastic demand). Conversely, a rise in the price of a packet of chewing gum has very little effect on demand because it represents a negligible portion of most consumers’ income (inelastic demand).
4. Time Period Considered (for Adjustment):
   • Short-term = More inelastic PED. In the short run, consumers may have limited options or insufficient time to find substitutes, adjust their consumption habits, or alter their behaviour in response to a price change.
   • Long-term = More elastic PED. Over a longer period, consumers have more time to search for and discover alternatives, modify their routines, or even invest in new technologies that reduce their reliance on the good. This makes their demand more responsive to price changes.
   • Example: A sudden, sharp increase in fuel prices may not immediately reduce demand for petrol (short-term inelasticity) as people still need to commute. However, over several months or years (long-term), consumers might respond by switching to public transport, carpooling, buying more fuel-efficient vehicles, or even transitioning to electric vehicles (making demand more elastic).
5. Addictiveness or Habitual Consumption:
   • Goods that are addictive (e.g., nicotine products, certain illicit drugs) or are consumed out of strong habit (e.g., daily coffee for a habitual drinker) tend to have highly inelastic demand. Consumers find it difficult to reduce consumption, even with substantial price increases, due to physical or psychological dependence.
   • Example: The demand for cigarettes is relatively inelastic, especially for long-term smokers, making them a common target for sin taxes by governments.

Check our our Economics Song on the Determinants of PED!

2. Price Elasticity of Supply (PES)

2.1 Definition

Price Elasticity of Supply (PES) measures the degree to which the quantity supplied of a good or service responds to a percentage change in its price, assuming all other factors remain constant. It indicates how sensitive producers are to price fluctuations.

2.2 Formula:

PES=% Change in Price% Change in Quantity Supplied

2.3 Interpretation of PES Values

• PES > 1 (Elastic Supply):
  • Interpretation: The percentage change in quantity supplied is greater than the percentage change in price. Producers are highly responsive to price changes; they can significantly increase output with a relatively small price rise.
  • Example: Easily manufactured goods with readily available inputs and existing spare production capacity, like basic t-shirts, simple plastic products, or software licenses.
• PES = 1 (Unitary Elastic Supply):
  • Interpretation: The percentage change in quantity supplied is equal to the percentage change in price.
  • Example: A producer that can proportionately increase output with a proportional price increase.
• PES < 1 (Inelastic Supply):
  • Interpretation: The percentage change in quantity supplied is less than the percentage change in price. Producers are relatively unresponsive; they find it difficult to significantly change output even with a large price change.
  • Example: Agricultural products in the short term (due to fixed growing cycles), highly specialised capital goods like custom-built ships, or rare artworks.
• PES = 0 (Perfectly Inelastic Supply):
  • Interpretation: Quantity supplied does not change at all, regardless of the price change. Supply is fixed.
  • Graphical Representation: The supply curve is a vertical line.
  • Example: The total number of seats in a fully booked concert venue for a specific event, or the original paintings by a deceased artist. (Supply is absolutely fixed.)
• PES = ∞ (Perfectly Elastic Supply):
  • Interpretation: Producers will supply any quantity at a specific price, but not at a slightly lower price. This implies infinite responsiveness to price at a given level.
  • Graphical Representation: The supply curve is a horizontal line.
  • Example: A single firm operating in a perfectly competitive market that can expand production indefinitely at a constant cost (theoretical).

2.4 Determinants of PES

The factors below determine how easily and quickly producers can adjust their output in response to price changes:

1. Length and Complexity of the Production Process / Production Lag:
   • Short and simple production processes = More elastic supply. If a good can be produced quickly with relatively simple methods (e.g., fast-food items, basic textiles), producers can rapidly adjust output in response to price changes.
   • Long and complex production processes / Long production lag = More inelastic supply. Goods that require significant time, multiple stages, or complex machinery to produce (e.g., custom-built aircraft, large-scale infrastructure projects, wine) have inelastic supply because adjustments require substantial time and resources.
   • Example: Bread production is relatively elastic as it involves a quick and straightforward process. In contrast, aeroplane manufacturing is highly inelastic due to its immense complexity, specialised components, and extremely long production lead times.
2. Availability and Mobility of Factors of Production:
   • More availability and mobility = More elastic supply. If factors like skilled labour, specific raw materials, or specialised machinery are readily available and can be easily and quickly reallocated from one use to another, supply will be more responsive to price changes.
   • Limited availability or immobility = More inelastic supply. If specialised inputs are scarce, difficult to obtain, or not easily transferable between industries, supply will be less responsive.
   • Example: An abundant supply of skilled IT workers in a booming technology sector increases the supply elasticity for software development services. Conversely, highly specialised industries like luxury watchmaking often face inelastic supply due to the limited number of highly skilled artisans and rare components.
3. Production Spare Capacity:
   • High spare capacity = More elastic supply. If a firm is operating below its full capacity (i.e., has unused machinery, idle labour, or empty production lines), it can easily increase output when prices rise without significant additional investment.
   • Low/no spare capacity = More inelastic supply. If a firm is operating near or at full capacity, it will be difficult and costly to increase production rapidly, even with a higher price, requiring new capital investment or expansion.
   • Example: A clothing factory with idle sewing machines and available workers can quickly increase its output of garments when prices rise, demonstrating elastic supply. A power plant already running at peak capacity, however, cannot immediately generate more electricity when demand spikes.
4. Ability to Store Goods (Perishability):
   • Non-perishable/easily storable goods = More elastic supply. If goods can be stored easily and cheaply (e.g., grains, canned goods, durable electronics), producers can hold back supply when prices are low and release it when prices rise, making their supply more flexible and responsive.
   • Perishable goods with limited storage options = More inelastic supply. Goods that spoil quickly or are very costly to store (e.g., fresh fish, ripe fruits, cut flowers) have less elastic supply, as producers must sell them quickly regardless of immediate price fluctuations to avoid spoilage.
   • Example: Non-perishable items like canned goods have a relatively elastic supply due to their long shelf life and ease of storage. Fresh produce like strawberries, however, has a more inelastic supply in the short term due to its limited storage capacity and rapid perishability.
5. Level of Stocks or Inventories:
   • High inventory levels = More elastic supply. Firms holding large stockpiles of finished products can respond very quickly to an increase in demand and price by releasing existing inventory into the market, making their supply more elastic in the short run.
   • Low inventory levels = More inelastic supply. Firms operating with minimal “just-in-time” inventory struggle to adjust supply rapidly to sudden price changes, making their supply relatively inelastic.
   • Example: A furniture manufacturer with a large warehouse full of finished products can easily meet a sudden surge in demand, demonstrating elastic supply from its existing stock.
6. Nature of Goods (Perishable vs. Non-Perishable) – Already covered in point 4, but can be a standalone point for emphasis if desired.
   • This reiterates the point that non-perishable goods offer greater flexibility for producers (elastic supply), while perishable goods inherently limit flexibility (inelastic supply).
   • Example: Canned fish can be stored and supplied to the market flexibly (elastic), whereas fresh fish has to be sold almost immediately after catch (inelastic).
7. Duration Considered (Most Important Factor):
   • Momentary/Immediate Run: Supply is perfectly inelastic (PES = 0). In this very short period, producers cannot adjust any factors of production; supply is fixed.
   • Short Run: Supply is often inelastic (PES < 1). Some variable inputs (e.g., labour, raw materials) can be adjusted, but fixed inputs (e.g., factory size, machinery) cannot. Firms can only slightly vary output.
   • Long Run: Supply becomes more elastic (PES > 1). All factors of production can be varied. Firms can build new factories, invest in new technologies, train more workers, or even enter/exit the industry, allowing for significant and flexible adjustments to supply.
   • Example: Farmers cannot immediately increase the supply of a specific crop if prices suddenly rise today (short-run inelasticity, as it takes a growing season). However, in the next growing season (long run), they can plant more of that crop, making the supply more elastic over time.

Revision Songs

Determinants of elasticity are pure recall, and recall is exactly what music is good for.

Mr Kelvin Hong’s price elasticity of demand song — definitions and determinants, in a format that survives exam-week cramming.

And the same treatment for the supply side.

Mr Kelvin Hong’s price elasticity of supply song — the determinants, including the role of time period and spare capacity.

3. Applications of PED and PES

This section moves beyond definitions to explore the practical applications of these price elasticity concepts, focusing on scenarios that lead to sharp changes in prices or quantities in real-world markets. Understanding these applications is critical for comprehending market dynamics and is especially relevant for students pursuing A-Level Economics.

3.1 Scenarios Leading to Sharp Changes in Prices

The magnitude of price and quantity changes following shifts in demand or supply is heavily dependent on the elasticities of the curves involved. When one or both curves are inelastic, even small shifts can lead to significant price volatility.

3.1.1 Demand Curve Shifts When Supply is Price Inelastic

When supply is price inelastic, it means that producers cannot significantly increase their quantity supplied in response to a price change. If, in such a market, there is an increase in demand, it will lead to a steep rise in prices because producers are unable to quickly or substantially expand output to meet the new demand. The limited responsiveness of supply forces the price to absorb most of the adjustment.

• Diagrammatic Illustration: Imagine a steep (inelastic) supply curve. A rightward shift of the demand curve will intersect the inelastic supply curve at a much higher price level, with only a small increase in quantity.
• Example: The housing market in land-scarce cities like Singapore or Hong Kong. Due to severe limitations on available land, lengthy planning and approval processes, and slow construction times, the supply of new housing units is typically very price inelastic, especially in the short to medium term. When there is a significant increase in population or wealth leading to higher demand for housing, the inelastic supply ensures that property prices surge dramatically, as seen in the continuous upward trend of HDB resale prices or private condo prices in Singapore.

3.1.2 Supply Curve Shifts When Demand is Price Inelastic

Conversely, if demand is price inelastic, it means that consumers are relatively unresponsive to price changes. In such a market, even a slight reduction in supply will result in a sharp increase in prices because consumers continue to demand almost the same quantity, even at higher prices. The limited responsiveness of demand forces the price to absorb most of the adjustment from the supply shock.

• Diagrammatic Illustration: Imagine a steep (inelastic) demand curve. A leftward shift of the supply curve will intersect the inelastic demand curve at a much higher price level, with only a small decrease in quantity.
• Example: The global oil market. Demand for oil, especially for transportation and industrial uses, tends to be price inelastic in the short run as there are few immediate substitutes or ways for consumers/businesses to drastically cut consumption. If there is a sudden drop in oil production (e.g., due to geopolitical conflict in the Middle East, natural disasters affecting oil rigs, or OPEC production cuts), this reduction in supply leads to a significant price increase per barrel, as observed during the 1970s oil crises or more recently with the Russia-Ukraine conflict.

3.1.3 Demand or Supply Shifts When Both Are Price Inelastic

When both demand and supply are price inelastic, any shift in either curve, even a relatively small one, will result in extreme price changes with only minimal changes in quantity. This creates highly volatile markets.

• Diagrammatic Illustration: Both the demand and supply curves are steep. A shift in either curve will cause the equilibrium price to change drastically, while the equilibrium quantity changes very little.
• Example: The market for certain critical medical supplies during the early stages of the COVID-19 pandemic. The demand for items like face masks, hand sanitisers, and ventilators became highly price inelastic (due to the perceived life-saving necessity and fear). Simultaneously, the short-run supply of these specialised goods was also highly inelastic (due to limited manufacturing capacity, specific raw material requirements, and global supply chain disruptions). The combined effect of this extremely high, inelastic demand and very low, inelastic supply caused prices to rise dramatically, leading to widespread shortages and price-gouging concerns globally.

3.2 Factors Explaining Large Changes in Price or Output

Beyond merely identifying when elasticities are low, a deeper qualitative and quantitative analysis helps explain the magnitude of these changes.

3.2.1 Qualitative Analysis

Understanding price and output changes also requires considering several qualitative factors that influence the underlying elasticities:

• Nature of the good:
  • Essentials/Necessities (e.g., electricity, basic food, water) tend to have more inelastic demand. When their supply is constrained (e.g., due to power plant outages, droughts), they are much more prone to sharp price volatility than luxuries.
  • Luxuries (e.g., high-end art, designer goods) tend to have more elastic demand. Price changes might lead to larger quantity changes rather than extreme price swings, as consumers can easily forgo them.
• Market Conditions/Structure:
  • Monopolistic or Oligopolistic markets (e.g., diamond mining controlled by a few large firms like De Beers, or certain pharmaceutical markets with patented drugs) tend to experience larger price swings or controlled output levels due to limited competition and significant market power, which influences elasticity.
  • Highly competitive markets with many substitutes tend to have more elastic demand for individual firms, leading to less individual firm price power.
• Time Horizon: As discussed with PED and PES determinants, the responsiveness of both demand and supply typically increases over longer time horizons, meaning price fluctuations might be less extreme in the long run compared to the short run.
• Government Intervention: Policies like price ceilings, price floors, taxes, or subsidies can distort natural market responses and affect the observed price and output changes.

3.2.2 Elasticities Analysis (Quantitative Approach)

Elasticities provide a quantitative way to analyse and predict the relative magnitude of price and output changes following shifts in demand or supply:

• If Demand is Inelastic (PED<1): A given leftward shift in supply (e.g., reduced production due to higher costs) will result in a significant increase in price but only a small decrease in quantity traded. Consumers absorb most of the price increase.
• If Supply is Inelastic (PES<1): A given rightward shift in demand (e.g., increased consumer preference) will result in a sharp increase in price but only a limited expansion in output. Producers cannot easily ramp up production to meet the new demand.
• If Both Demand and Supply are Inelastic, any shift in either curve will cause extreme price volatility with minimal changes in quantity traded. This creates highly unstable markets where small shocks have magnified price impacts.

Example Analysis:

• The 2008 global oil price spike (reaching nearly $150/barrel): This occurred due to a combination of factors: rapidly rising global demand (especially from emerging economies like China and India, making demand increasingly inelastic due to growing reliance) meeting a short-run inelastic supply (difficulty in rapidly increasing oil extraction and refining capacity). Geopolitical tensions and speculative trading amplified these underlying elasticities.
• Agricultural Markets: Markets for staple agricultural products (e.g., wheat, corn) frequently experience sharp price swings. This is largely because their short-run supply is highly inelastic (due to fixed growing seasons and limited ability to instantly change output). When coupled with weather-related disruptions (e.g., droughts, floods causing supply shocks) and relatively inelastic demand for basic food, even minor supply disruptions can lead to significant price spikes, impacting global food security.

3.3 Key Diagrams and Graphs for PED and PES

Visualising these concepts is crucial for understanding. Students should be able to draw and explain the following:

1. Inelastic Supply Curve with Rightward Demand Shift: Depict a steep supply curve. Show a rightward shift of the demand curve. The new equilibrium will show a large increase in price and a small increase in quantity.
2. Inelastic Demand Curve with Leftward Supply Shift: Depict a steep demand curve. Show a leftward shift of the supply curve. The new equilibrium will show a large increase in price and a small decrease in quantity.
3. Both Demand and Supply are Inelastic: Illustrate both curves as very steep. Show a shift in either curve to demonstrate the extreme price volatility with minimal quantity changes.

3.4 Real-World Case Studies for PED and PES

Applying elasticity concepts to specific markets helps solidify understanding.

3.4.1 Housing Markets

• Land-scarce cities such as Singapore, Hong Kong, and parts of London consistently experience high housing prices. A major contributing factor is the highly inelastic supply of housing (due to limited land, stringent zoning laws, and long construction lead times). Any sustained increase in demand (e.g., from population growth, foreign investment, or rising incomes) inevitably translates into sharp price increases rather than significant increases in new housing units.
• Government policies, such as Singapore’s “cooling measures” (e.g., Additional Buyer’s Stamp Duty, Seller’s Stamp Duty), are designed to influence the demand side (making it more elastic or reducing it) and stabilise prices, acknowledging the inelasticity of supply.

3.4.2 Oil Market

• The global oil market frequently serves as a textbook example of elasticity applications. Geopolitical events (e.g., conflicts in oil-producing regions like the Middle East or embargoes), natural disasters (e.g., hurricanes disrupting Gulf of Mexico oil production), or cartel decisions (e.g., OPEC production cuts) cause immediate supply shocks. Given the relatively inelastic short-run demand for oil (as discussed earlier), these supply disruptions invariably lead to significant price spikes. Conversely, global recessions reduce demand for oil (a leftward shift), leading to sharp price drops due to inelastic supply in the short run.

3.4.3 Healthcare Industry (during Crises)

• During the COVID-19 pandemic, the market for essential medical supplies (e.g., N95 masks, ventilators, specialised testing kits) perfectly illustrated the impact of inelasticities. There was an unprecedented and highly inelastic surge in demand globally due to the urgent need to control the virus and treat patients. Simultaneously, the supply of these specialised goods was highly inelastic in the short run, as manufacturers faced capacity constraints, raw material shortages, and complex production processes. This lethal combination led to unprecedented price increases and severe shortages globally, highlighting the critical role of elasticities in crisis management.

4. Summary for PED and PES

• Elasticity is a crucial measure of responsiveness that underpins the dynamics of supply and demand.
• Sharp price changes in markets often occur when either the supply or demand curve (or both) is price inelastic. Inelasticity implies limited ability to adjust quantity, forcing price to absorb most of the market adjustment following a shift.
• Understanding and applying elasticities, combined with a qualitative analysis of market conditions and specific goods, are essential for comprehending price and output fluctuations in real-world economic scenarios.
• These concepts are fundamental for analytical thinking in A-Level Economics and beyond.

Here are Summary Tables on PED and PES for a quick revision.

Even better, check out our Part 1 PED PES video here:

5. Income Elasticity of Demand (YED)

5.1 Definition of YED

Income Elasticity of Demand (YED) measures the responsiveness of the quantity demanded of a good or service to a percentage change in consumer income, assuming all other factors (including price) remain constant (ceteris paribus). It helps to classify goods based on how their demand changes with income.

5.2 Formula for YED

YED=% Change in Consumer Income% Change in Quantity Demanded

5.3 Interpretation of YED Sign and Value

The sign of YED (positive or negative) indicates the type of good, while its absolute value indicates the degree of responsiveness.

• Positive YED (YED > 0): Normal Goods
  • Interpretation: Demand for the good increases as consumer income rises. This is typical for most goods and services.
  • Graphical Effect: A rightward shift of the demand curve as income rises.
  • Example: Branded clothing, smartphones, and dining out at restaurants. As incomes grow in a country like Singapore, demand for such goods and services generally rises.
  • Sub-categories of Normal Goods:
    • Positive YED but Less Than 1 (0 < YED < 1): Income Inelastic Normal Goods (Necessities)
      • Interpretation: Demand for these goods increases with income, but proportionally less than the increase in income. These are goods considered necessities that people will always buy, but consumption doesn’t dramatically increase with higher income.
      • Example: Basic utilities like electricity or water, staple foods (e.g., rice, bread), and basic public transport. Even high-income households do not significantly increase their consumption of water beyond a certain point.
    • Positive YED Greater Than 1 (YED > 1): Income Elastic Normal Goods (Luxuries)
      • Interpretation: Demand for these goods increases more than proportionally to the increase in income. These are typically luxury goods or non-essentials.
      • Example: High-end cars (e.g., Tesla, Porsche), premium watches (e.g., Rolex), international luxury travel, private education. As incomes rise, consumers allocate a significantly larger proportion of their additional income to these items.
• Negative YED (YED < 0): Inferior Goods
  • Interpretation: Demand for the good decreases as consumer income rises. As incomes improve, consumers switch away from these goods to higher-quality or more preferred alternatives.
  • Graphical Effect: A leftward shift of the demand curve as income rises.
  • Example: Instant noodles, second-hand clothing, generic-brand groceries, or cheap public transport (when a private car becomes affordable). In many developing economies, as incomes rise, demand for these items often sees a reduction as people can afford better options.

5.4 Determinants of YED

Several factors influence YED values and the classification of goods:

1. Type of Good (as perceived by consumers): Whether a good is considered a luxury, necessity, or inferior good fundamentally determines its YED. This perception can vary across different income groups or cultures.
2. Economic Development of a Country: In developing economies, YED for many consumer goods (especially durable goods like appliances, cars, and electronics) is generally higher as incomes are growing rapidly from a lower base, leading to significant increases in demand as people move into higher income brackets.
3. Cultural Factors and Social Norms: Preferences for goods vary across different cultures, influencing how they are perceived as necessities or luxuries. For example, owning a car might be a necessity in some sprawling Western cities but a luxury in densely populated, public-transport-rich cities like Singapore.
4. Consumer Income Level (Absolute vs. Relative): The same good might be a luxury for a low-income household but a necessity for a high-income household. Higher-income households tend to show less sensitivity to income changes for necessities they already consume in sufficient quantities.

5.5 Applications of YED

Understanding YED is crucial for various economic agents:

1. Business Strategy (Firms):
   • Firms use YED to predict future changes in demand for their products and adjust their production and marketing strategies accordingly.
   • Example: Manufacturers of luxury vehicles (high positive YED) will closely monitor economic forecasts. During anticipated economic booms or periods of rising national income, they might proactively increase production capacity and launch new models, expecting a surge in demand. Conversely, during recessions, they might scale back production or focus on more “affordable luxury” lines.
   • Firms producing inferior goods (negative YED) might prepare for decreased demand during economic upturns and focus on cost efficiencies, or conversely, expand production during recessions.
2. Government Policy:
   • Governments analyse YED to understand how economic growth (or recession) will impact demand for different goods, which informs taxation, subsidies, and social welfare policies.
   • Example: Governments often provide subsidies for affordable housing or subsidised public transport (goods with low positive YED or even negative YED in some contexts for the poorest) to ensure accessibility for low-income groups. Understanding YED helps them target these subsidies effectively. Goods with high positive YED (luxuries) are often subject to higher taxes (e.g., luxury taxes, higher GST rates in some countries) as their consumption is less essential and provides greater tax revenue as incomes rise.

6. Cross Elasticity of Demand (XED)

6.1 Definition of XED

Cross Elasticity of Demand (XED) measures the responsiveness of the quantity demanded of one good (Good A) to a percentage change in the price of another related good (Good B), assuming all other factors remain constant. It helps to determine the relationship between two goods.

6.2 Formula for XED

XEDAB=% Change in Price of Good B% Change in Quantity Demanded of Good A

6.3 Interpretation of XED Sign and Value

The sign of XED determines whether goods are substitutes, complements, or unrelated. The absolute value indicates the strength of the relationship.

• Positive XED (XED > 0): Substitute Goods
  • Interpretation: An increase in the price of Good B leads to an increase in the demand for Good A. Consumers switch from the now more expensive Good B to its substitute, Good A.
  • Graphical Effect: A rightward shift of the demand curve for Good A when the price of Good B rises.
  • Example: If Coca-Cola’s price rises, consumers may switch brands, leading to an increase in demand for Pepsi. The higher the positive XED, the stronger the substitute relationship (e.g., butter and margarine have a very high positive XED).
• Negative XED (XED < 0): Complementary Goods
  • Interpretation: An increase in the price of Good B leads to a decrease in the demand for Good A. Since these goods are consumed together, if one becomes more expensive, demand for the other falls.
  • Graphical Effect: A leftward shift of the demand curve for Good A when the price of Good B rises.
  • Example: A significant drop in the price of gaming consoles (e.g., PlayStation) will make console ownership more affordable, thereby increasing the demand for video games (a complement).
• XED = 0: Unrelated Goods
  • Interpretation: A change in the price of Good B has no significant effect on the demand for Good A.
  • Example: The price of bananas is unlikely to affect the demand for laptops. Their markets are completely independent.

6.4 Determinants of XED

The strength and sign of XED are primarily influenced by:

1. Closeness of Substitutes/Complements:
   • The closer the goods are perceived as substitutes or complements by consumers, the higher the absolute value of XED.
   • Example: Butter and margarine are very close substitutes, exhibiting a strong positive XED. In contrast, while cars and bicycles are substitutes, they are not as close, so a rise in car prices may not lead to as dramatic an increase in bicycle demand as it might for another car brand.
2. Nature of Goods:
   • The fundamental nature of the goods defines their relationship. Are they consumed together (complements) or can one replace the other (substitutes)?
   • Example: The relationship between tea and coffee (substitutes) is clearly distinct from the relationship between cars and fuel (complements).
3. Consumer Perception and Information:
   • How closely consumers perceive the goods as related and their awareness of alternatives influence the XED. Marketing and branding can play a role here.

6.5 Applications of XED

XED is a vital tool for businesses and regulators:

1. Pricing Strategy (Firms):
   • Companies analyse XED to adjust their pricing strategies in response to competitors’ actions or changes in the price of complementary products.
   • Example: If a major competitor (e.g., Starbucks) lowers the price of its coffee, a rival coffee shop (e.g., Coffee Bean) must analyse the XED between their products. If XED is high and positive, they may need to launch similar discounts or promotions to retain customers and prevent a significant fall in their own demand.
2. Mergers and Acquisitions:
   • Businesses evaluate XED when considering mergers or acquisitions with related firms. A high positive XED might indicate that two companies are strong competitors (and a merger might raise antitrust concerns), while a negative XED might suggest a beneficial vertical integration opportunity.
   • Example: A phone manufacturer (like Apple) acquiring a software company or a music streaming service (e.g., buying Shazam) reflects an understanding of complementary goods, aiming to bundle products and enhance the overall ecosystem value for consumers.
3. Government Policy (Regulation, Taxation, Subsidies):
   • Regulators use XED to assess the impact of taxes, subsidies, or antitrust actions on related markets.
   • If a government taxes a good with a high positive XED (e.g., a tax on sugary drinks), it must anticipate that demand will shift significantly to substitute beverages.
   • Example: Competition authorities use XED to define relevant markets. If XED between two products is very high, they are strong substitutes, and a merger between their producers might lead to a monopoly and be blocked.

7. Real-World Examples for YED and XED

7.1 Income Elasticity of Demand (YED)

• In Singapore, with its rapidly rising average incomes over the past decades, there has been a sustained increase in demand for luxury condominiums (premium housing) and private cars. This clearly highlights their strong positive YED, as a greater proportion of rising income is spent on these aspirational goods.
• In developing economies like India, as per capita incomes grow significantly, there’s a high YED for consumer durables like two-wheelers (motorcycles/scooters) and smartphones, as these goods transition from being luxuries to more accessible items for a large segment of the population.

7.2 Cross Elasticity of Demand (XED)

• Substitutes in Singapore: If Grab ride-hailing prices hike significantly (e.g., due to increased surge pricing or fare adjustments), consumers in Singapore often exhibit a switch to public transportation (MRT/bus) or other ride-hailing apps, indicating a positive XED between these services.
• Complements: The continuous reduction in the cost of mobile data plans and broadband internet services globally has been a key factor driving the massive increase in demand for smartphones, tablets, and smart TVs, demonstrating a negative XED relationship between internet services and these complementary hardware devices.

8. Key Diagrams and Graphs for YED and XED

Understanding how YED and XED manifest graphically is crucial for analysis.

8.1 Income Elasticity Diagrams (YED)

• Normal Goods (YED > 0): An increase in consumer income leads to a rightward shift of the demand curve (e.g., from D1 to D2), indicating a higher quantity demanded at every price. For luxuries (YED > 1), this shift would be proportionally larger than for necessities (0 < YED < 1).
• Inferior Goods (YED < 0): An increase in consumer income leads to a leftward shift of the demand curve (e.g., from D1 to D2), indicating a lower quantity demanded at every price.

8.2 Cross Elasticity Diagrams (XED)

• Substitute Goods (Positive XED): If the price of Good B increases, the demand curve for Good A shifts rightward (e.g., from $D_A_1$ to $D_A_2$), indicating an increase in demand for Good A at every price.
• Complementary Goods (Negative XED): If the price of Good B increases, the demand curve for Good A shifts leftward (e.g., from $D_A_1$ to $D_A_2$), indicating a decrease in demand for Good A at every price.

9. Summary on XED and YED

• YED measures how income changes affect demand, classifying goods as normal goods (necessities and luxuries) or inferior goods. It is crucial for businesses to predict market growth and for governments to design effective tax and welfare policies.
• XED explains how the price of related goods (substitutes and complements) influences demand for a specific good. It is vital for understanding competitive relationships, pricing strategies, and merger analysis.

Businesses, governments, and students studying economics can apply these concepts to predict market dynamics, understand consumer behaviour, and make more informed decisions in a constantly evolving economic landscape.

10. Practice Questions

10.1 Short Answer Questions

• PED & Revenue: Explain the relationship between Price Elasticity of Demand (PED) and a firm’s Total Revenue. Using this relationship, determine whether a producer of a price-inelastic good should raise or lower prices to maximize revenue.
• Determinants of PED: How does the “availability of close substitutes” influence the PED value of a product? Provide examples of a good with many substitutes and a good with few substitutes.
• PES & Time: Define Price Elasticity of Supply (PES) and explain why the supply of most goods tends to be price inelastic in the short run but price elastic in the long run.
• YED (Necessities): Define Income Elasticity of Demand (YED) and explain its importance for goods considered necessities.
• XED (Substitutes/Complements): Differentiate clearly between a positive and a negative Cross Elasticity of Demand (XED), providing a distinct real-world example for each.

10.2 Application-Based Questions

• PED (Taxation): The government plans to impose a heavy tax on two goods: (a) Cigarettes and (b) Restaurant Meals. Using the concept of PED, explain which good would generate more tax revenue for the government and which good would see a larger drop in consumption.
• PES (Housing vs. Digital Goods): Compare the Price Elasticity of Supply for new private housing in a land-scarce city versus subscriptions for a video streaming service. Explain the key determinant responsible for the difference in their elasticity values.
• YED (Emerging Economies): Analyse how rising per capita incomes in a rapidly developing economy (e.g., Vietnam) might affect the demand for (a) instant noodles and (b) locally assembled private cars. Use the concept of YED in your explanation.
• XED (Transport Substitutes): Discuss how a significant price increase in public transportation fares in a major city like London might affect the demand for (a) private ride-hailing services (e.g., Uber/Grab) and (b) bicycle sales. Apply the concept of XED in your analysis.

---