Consumer behaviour is the study of how individuals, households, and groups select, purchase, and use goods and services to satisfy their needs and desires. In economic theory, this is rooted in the Theory of Consumer Choice, which examines the trade-offs consumers make when faced with limited income and various price points.
Core Postulates of Consumer Rationality
Economists assume the “Rational Consumer” model, which operates under specific logical constraints:
- Completeness: A consumer can rank all possible bundles of goods based on preference.
- Transitivity: If a consumer prefers bundle A to B, and B to C, then they must prefer A to C.
- Non-Satiation: Generally, “more is better”; a consumer will always prefer a bundle with more of at least one good, provided the quantity of other goods remains the same.
- Rationality: The primary objective is the maximization of total utility within the constraints of a fixed budget.
Determinants of Consumer Behaviour
Consumer decisions in India are influenced by a multifaceted set of factors that determine the aggregate demand curve:
| Determinant | Impact on Behaviour |
| Price of the Product | Usually follows the Law of Demand (inverse relationship). |
| Income Levels | Higher disposable income shifts demand from inferior to normal and luxury goods. |
| Price of Related Goods | Includes Substitutes (Tea vs. Coffee) and Complements (Cars and Petrol). |
| Tastes and Preferences | Influenced by cultural shifts, advertising, and seasonal changes. |
| Future Expectations | Expectations of price hikes lead to current hoarding or increased immediate demand. |
The Concept of Consumer Equilibrium
Consumer Equilibrium is the “point of rest” where a consumer derives maximum satisfaction from their expenditure. It is analyzed via two primary methods:
The Budget Line (Price Line)
The Budget Line represents all possible combinations of two goods that a consumer can purchase given their money income and the prices of the goods.
- The equation for the budget line is: PxQx + PyQy = M (where M is total income).
- A change in income causes a parallel shift in the budget line.
- A change in the price of one good causes a rotation of the budget line.
Indifference Map and Tangency
An Indifference Map is a family of Indifference Curves (IC). Equilibrium is reached at the point where the Budget Line is tangent to the highest possible Indifference Curve. At this point:
- The slope of the IC (Marginal Rate of Substitution) equals the slope of the Budget Line (Price Ratio).
- Formula: MRSxy = Px/Py.
Key Phenomena in Consumer Behaviour
The Income Effect
This refers to the change in demand resulting from a change in the consumer’s “real income” (purchasing power) due to a price change.
- For Normal Goods, the income effect is positive.
- For Inferior Goods, the income effect is negative.
The Substitution Effect
This occurs when consumers replace a more expensive item with a cheaper alternative following a price change, holding the level of utility constant. The substitution effect is always negative (demand moves opposite to price).
The Price Effect
The Price Effect is the net resultant of the Income Effect and the Substitution Effect.
- Price Effect = Substitution Effect + Income Effect.
Exceptions to Standard Consumer Behaviour
While most consumers follow the Law of Demand, certain goods trigger “anomalous” behaviour:
- Giffen Goods: Highly inferior goods where the negative income effect outweighs the substitution effect. When the price of a Giffen good (like a staple food in extreme poverty) rises, consumption actually increases because the consumer can no longer afford superior substitutes.
- Veblen Goods (Conspicuous Consumption): Goods consumed for status or prestige (e.g., luxury watches, designer diamonds). Demand increases as price increases because the “snob value” rises.
- Bandwagon Effect: When a consumer buys a product because others are buying it, regardless of its utility or price.
- Snob Effect: When a consumer stops buying a product because it has become too common.
Measuring Consumer Behaviour: Elasticity of Demand
Elasticity measures the responsiveness of the quantity demanded to a change in a determinant.
- Price Elasticity of Demand (Ep): Percentage change in quantity demanded divided by the percentage change in price.
- Unitary Elastic (Ep = 1): Total expenditure remains constant.
- Inelastic (Ep < 1): Essential goods (salt, medicines).
- Elastic (Ep > 1): Luxury goods (air conditioners, international travel).
- Income Elasticity (Ey): Measures responsiveness to income changes.
- Ey > 0: Normal Goods.
- Ey < 0: Inferior Goods.
- Ey > 1: Luxury Goods (Engel’s Law: As income rises, the proportion of income spent on food falls).
UPSC Fact-Sheet and Trivia
- Engel’s Law: Observations by Ernst Engel stating that as family income increases, the percentage of income spent on food decreases, even if total food expenditure increases. This is a key indicator of a country’s living standards.
- Consumer Surplus: The difference between the maximum price a consumer is willing to pay and the actual price paid (Total Utility – Total Expenditure). This concept is used by the Indian government to justify taxes and subsidies.
- The Paradox of Plenty: In years of bumper harvests in India, the price of crops falls so significantly that total revenue for farmers (producers/consumers of other goods) decreases due to inelastic demand for food grains.
- Nudge Theory: A concept in behavioural economics (popularized by Richard Thaler) suggesting that small interventions or “nudges” can influence consumer behaviour without restricting choices (e.g., placing healthy food at eye level in government-run canteens).