🛒Principles of Microeconomics Unit 6 – Consumer Choices

Key Concepts

• Consumer choice theory analyzes how consumers make decisions about purchasing goods and services based on their preferences, budget constraints, and the prices of goods
• Utility represents the satisfaction or benefit a consumer derives from consuming a good or service
• Marginal utility measures the additional satisfaction gained from consuming one more unit of a good or service
• Diminishing marginal utility states that as a consumer consumes more of a good, the additional satisfaction gained from each additional unit decreases
• Indifference curves represent all combinations of two goods that provide a consumer with the same level of satisfaction or utility
  • Indifference curves are downward sloping and convex to the origin
  • Higher indifference curves represent higher levels of utility
• Budget constraints represent the combinations of goods a consumer can afford given their income and the prices of the goods
• Optimal consumer choice occurs when a consumer maximizes their utility subject to their budget constraint

Consumer Preferences and Utility

• Consumer preferences describe how a consumer ranks different combinations of goods and services based on the satisfaction they provide
• Preferences are assumed to be complete (consumers can compare any two bundles), transitive (if A is preferred to B and B is preferred to C, then A is preferred to C), and more is always better
• Utility is a measure of the satisfaction or benefit a consumer derives from consuming a good or service
  • Utility is an ordinal concept, meaning it only represents relative rankings and not absolute values
• Marginal utility is the additional satisfaction gained from consuming one more unit of a good or service
• The law of diminishing marginal utility states that as a consumer consumes more of a good, the additional satisfaction gained from each additional unit decreases
• Indifference curves represent all combinations of two goods that provide a consumer with the same level of satisfaction or utility
  • Points along an indifference curve are considered equally desirable to the consumer
  • Indifference curves are downward sloping because to maintain the same level of utility, a decrease in the consumption of one good must be offset by an increase in the consumption of the other good

Budget Constraints

• A budget constraint represents the combinations of goods a consumer can afford given their income and the prices of the goods
• The budget constraint is a straight line with a slope equal to the negative of the ratio of the prices of the two goods ($-P_x/P_y$)
• The intercepts of the budget constraint represent the maximum amount of each good the consumer could purchase if they spent all their income on that good
  • The x-intercept is the consumer's income divided by the price of good x ($I/P_x$)
  • The y-intercept is the consumer's income divided by the price of good y ($I/P_y$)
• Changes in income shift the budget constraint parallel to the original constraint
  • An increase in income shifts the budget constraint outward
  • A decrease in income shifts the budget constraint inward
• Changes in the price of a good rotate the budget constraint around the intercept of the other good
  • A decrease in the price of a good makes the budget constraint flatter
  • An increase in the price of a good makes the budget constraint steeper

Optimal Consumer Choice

• Optimal consumer choice occurs when a consumer maximizes their utility subject to their budget constraint
• At the optimal choice, the consumer's indifference curve is tangent to their budget constraint
  • This means that the marginal rate of substitution (MRS) is equal to the price ratio of the two goods ($MRS = P_x/P_y$)
  • The MRS measures the rate at which a consumer is willing to trade one good for the other while maintaining the same level of utility
• The optimal choice represents the combination of goods that provides the consumer with the highest level of utility they can achieve given their budget constraint
• Corner solutions occur when the optimal choice involves consuming only one of the two goods
  • This happens when the MRS is not equal to the price ratio at any point along the budget constraint
• Interior solutions occur when the optimal choice involves consuming positive amounts of both goods

Income and Substitution Effects

• The income effect describes how a consumer's optimal choice changes when their income changes, holding prices constant
  • A normal good is one for which demand increases as income increases
  • An inferior good is one for which demand decreases as income increases
• The substitution effect describes how a consumer's optimal choice changes when the price of a good changes, holding utility constant
  • The substitution effect always leads to an increase in the consumption of the good whose price decreased and a decrease in the consumption of the good whose price increased
• The total effect of a price change on a consumer's optimal choice is the sum of the income and substitution effects
  • For normal goods, the income and substitution effects work in the same direction
  • For inferior goods, the income and substitution effects work in opposite directions, and the total effect depends on which effect dominates

Consumer Demand

• Individual demand curves show the relationship between the price of a good and the quantity demanded by a single consumer, holding all other factors constant
  • Individual demand curves are derived from the consumer's optimal choices at different prices
• Market demand curves show the relationship between the price of a good and the total quantity demanded by all consumers in the market
  • Market demand curves are derived by horizontally summing the individual demand curves of all consumers in the market
• The law of demand states that, all else being equal, as the price of a good increases, the quantity demanded decreases, and as the price of a good decreases, the quantity demanded increases
• The price elasticity of demand measures the responsiveness of the quantity demanded to changes in the price of a good
  • Elastic demand occurs when the percentage change in quantity demanded is greater than the percentage change in price ($|E_d| > 1$)
  • Inelastic demand occurs when the percentage change in quantity demanded is less than the percentage change in price ($|E_d| < 1$)
  • Unit elastic demand occurs when the percentage change in quantity demanded is equal to the percentage change in price ($|E_d| = 1$)

Applications and Real-World Examples

• Consumer choice theory can be applied to a wide range of real-world situations, such as:
  • Choosing between different brands of a product (Coke vs. Pepsi)
  • Deciding how to allocate time between work and leisure
  • Determining the optimal mix of goods and services to consume given a limited budget
• Income and substitution effects can help explain consumer behavior in response to price changes
  • For example, when the price of gasoline increases, consumers may switch to more fuel-efficient vehicles (substitution effect) or reduce their overall driving (income effect)
• Price elasticity of demand has important implications for businesses and policymakers
  • For goods with elastic demand (luxury goods), a small change in price can lead to a large change in quantity demanded, affecting total revenue
  • For goods with inelastic demand (necessities), a change in price has a smaller impact on quantity demanded, and total revenue moves in the same direction as the price change

Common Pitfalls and Study Tips

• Remember that utility is an ordinal concept and cannot be directly measured or compared across individuals
• Be careful not to confuse the budget constraint with the indifference curve; the budget constraint represents what the consumer can afford, while the indifference curve represents what the consumer prefers
• When analyzing the effects of price changes, always consider both the income and substitution effects and how they might work together or in opposite directions
• Pay attention to the units and interpretation of the price elasticity of demand; it is a unitless measure that represents the percentage change in quantity demanded for a given percentage change in price
• Practice graphing and interpreting indifference curves and budget constraints to better understand how changes in income and prices affect consumer choices
• When studying consumer demand, make sure to distinguish between individual demand curves and market demand curves and understand how they are related
• Always consider the ceteris paribus assumption (all else being equal) when analyzing consumer behavior and market outcomes