ECO415Ch2.3MidPoint

Summary

The video introduces elasticity of demand, focusing mainly on price elasticity of demand (PED), how to calculate it using the midpoint method, and how elasticity helps sellers predict the effect of price changes on total revenue.

Types of Demand Elasticity

The instructor identifies three types:

• Price elasticity of demand: How responsive the quantity demanded of a good is to a change in that good’s price.
• Cross elasticity of demand: How the quantity demanded of one good responds to a change in the price of another good.
• Income elasticity of demand: How the quantity demanded of a good responds to a change in consumers’ income.

The lesson develops PED in detail. The other elasticity topics, along with price elasticity of supply, are slated for later instruction.

Price Elasticity of Demand

PED measures how strongly buyers change the quantity they demand when a good’s price changes.

• Elastic demand: Buyers are relatively sensitive to price changes. A relatively small price change leads to a relatively large change in quantity demanded.
• Inelastic demand: Buyers are relatively insensitive to price changes. Even a substantial price change leads to a relatively small change in quantity demanded.

The coefficient is commonly interpreted using its absolute value:

• PED > 1: Elastic demand.
• PED = 1: Unit or unitary elasticity.
• PED < 1: Inelastic demand.
• PED = 0: Perfectly inelastic demand; quantity demanded does not change as price changes.
• PED = ∞: Perfectly elastic demand; even a slight price change is associated with an extremely large change in quantity demanded.

On a standard graph, price is on the vertical axis and quantity demanded is on the horizontal axis. Perfectly inelastic demand is drawn as a vertical line, while perfectly elastic demand is drawn as a horizontal line.

Calculating Elasticity

When percentage changes are supplied, the basic formula is:

[ \text{PED} = \frac{\%\text{ change in quantity demanded}} {\%\text{ change in price}} ]

The instructor notes that percentage-based elasticity is unit-free, making it easier to compare responsiveness across goods measured in different units.

When a question gives two prices and two quantities, the lesson uses the midpoint formula, also called arc elasticity:

[ \text{PED} = \frac{(Q_2-Q_1)/[(Q_2+Q_1)/2]} {(P_2-P_1)/[(P_2+P_1)/2]} ]

Here, (Q_1) and (P_1) are the initial quantity and price, while (Q_2) and (P_2) are the new quantity and price. The averages in the denominator of each percentage change use the midpoint of the two observations.

The instructor recommends this approach because it provides a consistent measure between two points rather than relying only on the initial value. Either rearranged version of the formula gives the same result.

For the other elasticity measures, the denominator changes: cross elasticity uses the percentage change in the price of another good, while income elasticity uses the percentage change in income.

The Total Revenue Test

Total revenue is:

[ \text{Total revenue (TR)} = \text{Price} \times \text{Quantity sold} ]

The test helps sellers anticipate whether a price change will increase or reduce revenue:

• Elastic demand: Price and total revenue move in opposite directions.
  • Lowering price tends to increase total revenue.
  • Raising price tends to decrease total revenue.
• Inelastic demand: Price and total revenue move in the same direction.
  • Lowering price tends to decrease total revenue.
  • Raising price tends to increase total revenue.
• Unit-elastic demand: A price change leaves total revenue unchanged, assuming the change in quantity offsets the price change proportionately.

For an elastic good, a price reduction is accompanied by a large enough increase in quantity sold to raise revenue. For an inelastic good, lowering the price increases quantity by too little to make up for the lower price, so revenue falls.

A further example plots total revenue at different prices and quantities. Total revenue rises over the elastic range, reaches its maximum around unit elasticity, and then falls over the inelastic range, producing an inverted-U-shaped total-revenue curve. The examples show why sellers should consider demand elasticity when choosing prices.

Factors Affecting Price Elasticity of Demand

• Availability of substitutes

  • More substitutes make demand more elastic because buyers can switch to alternatives if a good becomes more expensive.
  • Fewer substitutes make demand more inelastic.
  • Examples include similar chocolate-drink brands as substitutes and specialized brass polish as a product with fewer alternatives.

• Proportion of income spent on the good

  • Goods that take up a larger share of a buyer’s income tend to have more elastic demand because a price rise has a more noticeable financial impact.
  • Goods that account for only a small share of income tend to have more inelastic demand. The instructor gives toothpaste as an example.

• Luxury versus necessity

  • Luxury goods tend to have more elastic demand because buyers can more readily forgo or change those purchases when prices rise.
  • Necessities tend to have more inelastic demand because people continue to need them despite price changes. Examples include basic food, clothing, transportation, and education.

• Time available to adjust

  • Demand is often more inelastic in the short run, when buyers have little time to find alternatives or change habits.
  • Over the longer run, buyers have more opportunity to adjust, so demand tends to become more elastic.

The lecture also contrasts example goods and services with relatively inelastic and elastic demand. Its broad point is that basic or habitual purchases often have fewer practical short-run alternatives, while some higher-cost or more discretionary purchases may be more responsive to price.

Applications

• Sellers can use elasticity to choose prices that better support total revenue.
• Governments may be able to raise more tax revenue by imposing higher excise taxes on goods with inelastic demand, since buyers are less likely to reduce purchases substantially.
• In markets for necessities with inelastic demand, large crop yields can push prices down and may also reduce total revenue.

Speakers and Sources

• Speaker: The instructor/lecturer, identified by the channel as Nurhani Aba Ibrahim.
• Source cited in the lecture: McConnell, Brue, and Flynn, the economics textbook associated with the chapter on elasticity.