flowchart LR
PD[Price decrease] --> SE[Substitution effect<br/>X cheaper vs substitutes]
PD --> IE[Income effect<br/>Real income rises]
SE --> Q[Quantity demanded<br/>increases]
IE --> Q
classDef default fill:#003366,color:#ffffff,stroke:#ffcc00,stroke-width:3px,rx:10px,ry:10px;
8 Demand Analysis — Utility, Indifference Curves, Elasticity and Forecasting
8.1 What is Demand?
In everyday language, demand often means desire. In economics it is more disciplined: demand is the quantity of a good or service a consumer is willing and able to buy at a given price during a given period of time, ceteris paribus. Three elements distinguish demand from mere wanting:
- Willingness — the consumer wants the good.
- Ability — the consumer can pay for it.
- A definite price and time period — demand is a flow concept, measured per day, week or year.
A demand schedule tabulates the price–quantity relationship; a demand curve is its graphical form (downward sloping in normal goods).
TipDeterminants of demand
- Price of the good (Dₓ = f(Pₓ))
- Income of the consumer
- Prices of related goods (substitutes & complements)
- Tastes, preferences, advertising
- Number of consumers / population
- Expectations about future prices
- Distribution of income
- Climate, season, demographic structure
NoteDemand vs Quantity demanded — a crucial distinction
- Change in quantity demanded = movement along the same demand curve, caused by a change in own price.
- Change in demand = shift of the entire demand curve, caused by a change in any other determinant (income, tastes, related prices, etc.).
8.2 The Law of Demand
The most-tested proposition in economics: other things remaining the same, the quantity demanded of a good rises when its price falls and falls when its price rises — Marshall (Principles, 1890). The relationship is inverse.
Two effects drive the law:
- Substitution effect — when price of X falls, X becomes cheaper relative to substitutes; consumers shift from substitutes to X.
- Income effect — a price fall raises the consumer’s real income; if X is a normal good, more of it is bought.
8.2.1 Exceptions to the Law
TipWhere the Law of Demand breaks down
| Exception | Mechanism | Example |
|---|---|---|
| Giffen goods | Inferior goods so dominant in a poor consumer’s budget that the (negative) income effect outweighs the substitution effect | Sir Robert Giffen — 19th-century bread; potatoes in Irish famine |
| Veblen / conspicuous goods | Higher price → higher status → more demand | Luxury watches, designer handbags (Thorstein Veblen, Theory of the Leisure Class, 1899) |
| Speculative demand | Expectation of further rise | Shares, bullion, real estate in a bull market |
| Necessities of life | Demand insensitive to price changes | Salt, medicines (no substitutes) |
| Ignorance / brand loyalty | Consumers equate high price with high quality | Premium brand purchases without comparison |
NoteGiffen vs Veblen — PYQ trap
- Giffen goods are inferior — bought by the poor; reverse relationship because the income effect dominates.
- Veblen goods are luxury / status — bought by the rich; reverse relationship because of snob utility.
8.3 Types of Demand
TipUseful demand classifications
| Basis | Categories |
|---|---|
| Consumer | Individual demand · Market (industry) demand |
| Period | Short-run · Long-run |
| Goods type | Producer demand (derived) · Consumer demand (direct) |
| Substitutability | Substitute goods · Complementary goods · Independent goods |
| Time period | Perishable (immediate) · Durable (over time) |
| Number of goods consumed jointly | Joint demand · Composite demand · Derived demand · Autonomous demand |
NoteJoint vs Composite vs Derived
- Joint demand — two goods consumed together (car + petrol).
- Composite demand — same good has multiple uses (steel for cars, ships, bridges).
- Derived demand — demand for an input derived from demand for the final good (demand for steel derived from demand for cars).
8.4 Utility Analysis — Cardinal Approach (Marshall)
Alfred Marshall and the neo-classical economists assumed utility is cardinally measurable in units called utils. The two key laws:
8.4.1 Law of Diminishing Marginal Utility (DMU) — Gossen’s First Law
As a consumer consumes more units of a good, the additional (marginal) utility from each successive unit falls. Marshall: “the additional benefit which a person derives from a given increase in his stock of a thing diminishes with every increase in the stock that he already has.”
TipHidden assumptions of DMU
- Units of the good are homogeneous.
- Consumption is continuous (no break).
- Income, tastes and prices of related goods are constant.
- The good is not an addictive or rare collector’s item.
8.4.2 Law of Equi-marginal Utility — Gossen’s Second Law
A consumer allocates income across goods to equalise the marginal utility per rupee across all goods:
\[\frac{MU_X}{P_X} = \frac{MU_Y}{P_Y} = \ldots = \frac{MU_n}{P_n}\]
This is the consumer’s equilibrium condition under cardinal utility. The same principle underlies factor allocation by the firm (Topic 6).
8.4.3 Consumer Surplus
Marshall’s measure of buyer’s gain: the excess of what the consumer would have been willing to pay over what she actually pays — the area between the demand curve and the price line.
8.5 Indifference Curve Analysis — Ordinal Approach (Hicks-Allen)
Vilfredo Pareto, J.R. Hicks and R.G.D. Allen (Economica, 1934) replaced cardinal utility with ordinal preferences — the consumer can rank baskets but not assign numerical utils.
TipProperties of indifference curves
| Property | Meaning |
|---|---|
| Downward sloping | More of X requires less of Y to keep utility constant |
| Convex to origin | Diminishing Marginal Rate of Substitution (MRS) |
| Do not intersect | Two intersecting curves would imply two utility levels at one point — contradiction |
| Higher IC = higher utility | More is preferred to less |
| Cannot be thick | A thick curve would mean indifference between baskets of unequal quantity |
The Marginal Rate of Substitution (MRS) is the rate at which the consumer is willing to give up Y for one more unit of X while staying on the same IC. MRS = MUₓ / MUᵧ and diminishes as more X is consumed.
8.5.1 Budget line and consumer equilibrium
The budget line has slope = −Pₓ/Pᵧ. Consumer equilibrium is where the highest attainable indifference curve is tangent to the budget line, i.e.,
\[MRS_{XY} = \frac{P_X}{P_Y}\]
8.5.2 Hicks’s decomposition of price effect
Hicks decomposed the total price effect of a price change into:
- Substitution effect — change in quantity when relative prices change with real income held constant (always negative for the good whose price falls).
- Income effect — change in quantity due to change in real income with prices held at the new ratio.
The sum of the two = total price effect. For Giffen goods the income effect is negative and dominates the substitution effect — the demand curve slopes upward.
8.6 Elasticity of Demand
Elasticity measures the responsiveness of demand to changes in price, income, or related-good prices. Coined by Marshall, generalised by R.G.D. Allen.
TipFour kinds of elasticity
| Type | Formula | Measures |
|---|---|---|
| Price elasticity of demand (Eₚ) | (% ΔQ) / (% ΔP) | Response of demand to own price change |
| Income elasticity of demand (E_Y) | (% ΔQ) / (% ΔY) | Response of demand to income change |
| Cross elasticity of demand (E_XY) | (% ΔQₓ) / (% ΔPᵧ) | Response of Qₓ to price change of related good Y |
| Advertising elasticity | (% ΔQ) / (% Δ Advertising spend) | Response of demand to ad spend |
8.6.1 Price Elasticity — five degrees
TipFive degrees of price elasticity
| Magnitude | Name | Curve shape | Example |
|---|---|---|---|
| Eₚ = 0 | Perfectly inelastic | Vertical | Life-saving drug |
| 0 < Eₚ < 1 | Inelastic / relatively inelastic | Steep | Salt, electricity |
| Eₚ = 1 | Unitary elastic | Rectangular hyperbola | Total revenue unchanged |
| 1 < Eₚ < ∞ | Elastic / relatively elastic | Flat | Luxury goods, branded clothing |
| Eₚ = ∞ | Perfectly elastic | Horizontal | Firm in perfect competition |
NoteSign convention
Demand elasticities are reported as absolute values. The minus sign that strict economics requires is conventionally dropped: “Eₚ = 1.5” means a 1 % price rise cuts demand by 1.5 %.
8.6.2 Methods of measuring price elasticity
TipFive measurement methods
- Percentage method (Arc elasticity) — (% ΔQ) / (% ΔP). Used for finite changes; average of initial and final values.
- Total Outlay (TR) method — Marshall: if TR rises when price falls, demand is elastic; if TR is unchanged, unitary; if TR falls, inelastic.
- Point elasticity — slope of demand curve at a point; uses calculus dQ/dP × P/Q.
- Geometric method — for a straight-line demand curve, Eₚ at any point = lower segment / upper segment.
- Revenue method — derived from MR: MR = P(1 − 1/Eₚ).
NoteTR–Eₚ rule (Marshall) — memorise
- Eₚ > 1: price ↓ → TR ↑; price ↑ → TR ↓ (price and TR move opposite).
- Eₚ = 1: TR constant regardless of price change.
- Eₚ < 1: price ↓ → TR ↓; price ↑ → TR ↑ (price and TR move same direction).
8.6.3 Income Elasticity — classification of goods
TipE_Y signs classify goods
| Range of E_Y | Type of good | Example |
|---|---|---|
| Negative | Inferior | Coarse grains, second-hand clothes |
| Zero | Neutral / necessity at saturation | Salt at saturation |
| 0 < E_Y < 1 | Normal necessity | Food, basic clothing |
| E_Y = 1 | Unitary; rises in proportion to income | Standard consumer goods |
| E_Y > 1 | Luxury / superior | Cars, foreign holidays |
8.6.4 Cross Elasticity — substitutes and complements
TipE_XY signs classify relationships
| Sign of E_XY | Relationship | Example |
|---|---|---|
| Positive | Substitutes | Tea and coffee |
| Negative | Complements | Car and petrol; printer and cartridges |
| Zero | Independent | Salt and clothing |
8.6.5 Determinants of Price Elasticity
TipWhat makes demand more elastic?
- Availability of close substitutes — more substitutes → more elastic.
- Necessity vs luxury — necessities are inelastic; luxuries are elastic.
- Share in budget — large-share goods are more elastic.
- Time horizon — longer time → more substitutes available → more elastic.
- Definition of the market — narrower market (Honda Civic) is more elastic than broader (passenger cars).
- Habit / addiction — habit-forming goods are inelastic (tobacco).
8.7 Demand Forecasting
Demand forecasting estimates future demand to plan production, capacity, inventory and finance. Forecasts are classified by time horizon, level, and method.
8.7.1 By time horizon
- Short-term (less than 1 year) — production scheduling, working-capital planning.
- Medium-term (1–3 years) — sales budgets, raw-material contracts.
- Long-term (3+ years) — capacity planning, new-product launch, capital expenditure.
8.7.2 Methods — Qualitative vs Quantitative
TipQualitative methods (Survey)
| Method | What it does | Use case |
|---|---|---|
| Consumer Survey (complete enumeration or sample) | Ask intended buyers | New product launch |
| Sales Force Opinion | Aggregate field salespeople’s estimates | Quick short-term forecast |
| Expert Opinion (Delphi technique) | Iterative anonymous expert questionnaires (Helmer-Dalkey, RAND) | Long-term / technology forecasts |
| Market Experiment | Test-market the product in a limited area | New product or pricing |
TipQuantitative methods (Statistical)
| Method | Tool | Strength |
|---|---|---|
| Time-series — Trend projection | Fit a trend line to past sales | Simple, stable products |
| Time-series — Moving averages | Average last n periods | Smooths random fluctuations |
| Time-series — Exponential smoothing | Weighted averages giving more weight to recent | Adapts to recent changes |
| Decomposition | Trend + Seasonal + Cyclical + Irregular | When seasonality is strong |
| Box-Jenkins ARIMA | Auto-regressive integrated moving average | Sophisticated time-series |
| Barometric / Leading indicators | Use leading indicators (housing starts, PMI) | Macro / industry-wide |
| Econometric (Regression) | Causal relationship Q = f(P, Y, A, …) | Best when relationships are stable |
| Input-output analysis | Wassily Leontief — sectoral interdependence | Policy / national plans |
8.7.3 Survey methods — pros and cons
TipSurvey methods — at a glance
| Method | Strength | Weakness |
|---|---|---|
| Complete enumeration | Most accurate if respondents are honest | Costly, slow |
| Sample survey | Faster, cheaper | Sampling error |
| End-use method | Bottom-up; sectoral demand summed | Needs detailed data |
8.7.4 Criteria for a Good Forecast
TipCriteria — five tests
- Accuracy — closeness to actual outcome.
- Plausibility — managers must find it credible.
- Durability — useful for the planning horizon.
- Flexibility — adaptable when conditions change.
- Economy — cost of forecast < value of better decision.
NoteCommon forecasting errors
- Optimism bias — overestimating future sales.
- Trend extrapolation in a turning point — straight-line projections through a recession.
- Ignoring structural change — new entrants, technology, regulation.
- Insufficient triangulation — relying on a single method.
8.8 Practice Questions
Q 01
Definition
Easy
For a consumer's wish to count as *demand* in economics, it must be:
View solution
Correct Option: B
Demand = willingness + ability to buy at a given price and time. Mere desire is not demand.
Q 02
Change in Demand
Medium
A rise in consumer income causes the entire demand curve to shift right. This is a:
View solution
Correct Option: B
A *change in demand* shifts the entire curve and is caused by any non-price determinant. *Change in quantity demanded* is movement along the curve due to own-price change.
Q 03
Giffen
Medium
A *Giffen good* is an exception to the law of demand because:
View solution
Correct Option: B
A Giffen good is a *strongly inferior* good; the negative income effect outweighs the substitution effect, so price ↑ → quantity ↑. Sir Robert Giffen, 19th-century bread.
Q 04
Veblen
Medium
Veblen goods violate the law of demand because:
View solution
Correct Option: B
Thorstein Veblen's *Theory of the Leisure Class* (1899) — *conspicuous consumption*. Higher price → higher signalling utility → higher demand.
Q 05
DMU
Easy
The Law of Diminishing Marginal Utility is also known as:
View solution
Correct Option: A
Hermann Gossen's First Law (1854) = DMU. Second Law = Equi-marginal utility. Engel's Law is about food share falling as income rises.
Q 06
Equilibrium
Medium
In indifference-curve analysis, consumer equilibrium occurs where:
View solution
Correct Option: B
Consumer equilibrium: highest IC tangent to budget line → MRS_XY = Pₓ/Pᵧ, equivalently MUₓ/Pₓ = MUᵧ/Pᵧ.
Q 07
IC Properties
Medium
Indifference curves are *convex to the origin* because of:
View solution
Correct Option: B
Convexity reflects the diminishing MRS — the more X the consumer has, the less Y she is willing to give up for one more X.
Q 08
Elasticity Calc
Hard
Price of a good rises from ₹100 to ₹110 and quantity demanded falls from 50 to 45 units. The price elasticity of demand is:
View solution
Correct Option: B
% ΔQ = −5/50 = −10 %. % ΔP = 10/100 = +10 %. Eₚ = |−10/10| = 1.0 — unitary elastic.
Q 09
TR Test
Medium
When demand is *inelastic* (Eₚ < 1), a price *increase* will cause Total Revenue to:
View solution
Correct Option: C
Eₚ < 1: price and TR move in the same direction. Eₚ > 1: they move opposite. Eₚ = 1: TR unchanged.
Q 10
Income Elasticity
Medium
A good with *negative* income elasticity is classified as:
View solution
Correct Option: C
E_Y < 0 → as income rises, demand *falls* → inferior good. Coarse grains, second-hand clothes. E_Y > 1 → luxury.
Q 11
Cross Elasticity
Medium
A *negative* cross-price elasticity between two goods means they are:
View solution
Correct Option: B
E_XY < 0 → rising P of Y reduces Q of X → complements (car & petrol). Positive cross elasticity → substitutes (tea & coffee).
Q 12
Derived
Easy
Demand for steel arises from demand for cars, ships and buildings. This is an example of:
View solution
Correct Option: B
Composite demand — same good has multiple uses. *Derived* demand is when demand for one good follows from demand for another (steel demand derived from car demand — *also* arguable here). Best fit by the wording "*from demand for cars, ships and buildings*" is composite.
Q 13
Engel's Law
Hard
Engel's Law states that as income rises:
View solution
Correct Option: B
Ernst Engel (1857) — as household income rises, the *share* of spending on food falls, although the absolute amount may rise.
Q 14
Determinants of Elasticity
Medium
Demand for salt is *inelastic* primarily because:
View solution
Correct Option: B
Small budget share + no close substitutes + necessity → inelastic demand.
Q 15
Forecasting
Medium
The Delphi technique of forecasting:
View solution
Correct Option: B
Delphi (Helmer & Dalkey, RAND, 1959) — iterative *anonymous* expert questionnaires with controlled feedback.
Q 16
Time Series
Medium
A time-series demand forecast that gives *more weight to recent observations* is:
View solution
Correct Option: B
Exponential smoothing applies exponentially decreasing weights to older data — adapts faster to recent changes than a simple moving average.
Q 17
Methods
Medium
Match each demand-forecasting method with its family:
| (i) | Delphi | (a) | Time-series |
| (ii) | Moving average | (b) | Causal / econometric |
| (iii) | Regression | (c) | Qualitative / survey |
| (iv) | Barometric | (d) | Leading-indicator |
View solution
Correct Option: A
Delphi — qualitative/survey; Moving average — time-series; Regression — causal/econometric; Barometric — leading indicators.
Q 18
Hicks
Hard
Hicks's decomposition of the total price effect into substitution and income components rests on:
View solution
Correct Option: B
Hicks and Allen (1934) used ordinal preferences and indifference curves to decompose the price effect. Samuelson's *revealed preference* (1938) is an alternative approach.
Q 19
Five Degrees
Medium
A perfectly inelastic demand curve is:
View solution
Correct Option: B
Eₚ = 0 → quantity does not respond to price → vertical. Eₚ = ∞ → horizontal. Unitary elastic → rectangular hyperbola.
Q 20
Match Concepts
Hard
Match the concept with its origin:
| (i) | Consumer Surplus | (a) | Engel |
| (ii) | Indifference Curves | (b) | Marshall |
| (iii) | Conspicuous Consumption | (c) | Veblen |
| (iv) | Income-share of food falls with income | (d) | Pareto / Hicks-Allen |
View solution
Correct Option: A
Consumer Surplus — Marshall; Indifference Curves — Pareto/Hicks-Allen; Conspicuous Consumption — Veblen; Engel's Law — Engel.
8.8.1 Advanced Format Questions
AR 1Assertion-ReasonHard
A: Demand curve slopes downward.
R: Law of diminishing marginal utility.
View solution
Correct Option: A
AR 2Assertion-ReasonMedium
A: Giffen goods violate the law of demand.
R: They are essential inferior goods where income effect outweighs substitution effect.
View solution
Correct Option: A
N 1NumericalMedium
Price falls from ₹10 to ₹8; quantity demanded rises from 100 to 120. Price elasticity (arc method) is approximately:
View solution
Correct Option: A
Arc Ed = (ΔQ/avg Q) ÷ (ΔP/avg P) = (20/110) ÷ (2/9) ≈ 0.18/0.22 ≈ 0.82.
S 1Statement-basedMedium
Which elasticities exist? (i) Price. (ii) Income. (iii) Cross. (iv) Advertising.
View solution
Correct Option: A
8.9 Quick Recall
ImportantQuick recall
- Demand = willingness + ability to buy at a price & period (ceteris paribus). Demand vs Quantity demanded — shift vs movement.
- Law of demand — inverse P–Q relationship (Marshall). Drivers: substitution + income effects.
- Exceptions: Giffen (inferior, poor) · Veblen (conspicuous, rich) · Speculation · Necessities · Ignorance.
- Demand types: Joint · Composite · Derived · Autonomous; Individual vs Market; Short-run vs Long-run.
- Cardinal / Utility analysis (Marshall): DMU = Gossen’s 1st Law; Equi-marginal (MUₓ/Pₓ = MUᵧ/Pᵧ) = Gossen’s 2nd Law; Consumer surplus = Marshall.
- Ordinal / Indifference analysis (Pareto · Hicks-Allen 1934): IC properties; equilibrium MRS = Pₓ/Pᵧ. Hicks decomposed price effect into substitution + income components.
- Engel’s Law (1857): food share of income falls as income rises.
- Elasticity: Eₚ (own-price), E_Y (income), E_XY (cross), advertising. Five degrees (0, <1, =1, >1, ∞).
- TR–Eₚ rule (Marshall): Eₚ > 1 → P↑ shrinks TR; Eₚ = 1 → TR fixed; Eₚ < 1 → P↑ grows TR.
- E_Y signs: < 0 inferior; 0–1 necessity; > 1 luxury. E_XY: + substitutes; − complements; 0 independent.
- Forecasting methods — Qualitative (Consumer survey, Sales force, Delphi, Market experiment) · Quantitative (Trend, Moving avg, Exponential smoothing, ARIMA, Regression, Barometric, Input-output).
- Criteria of a good forecast: Accuracy · Plausibility · Durability · Flexibility · Economy.