Economics Study Notes: Demand Dynamics, Price Elasticity, and Total Revenue

Demand Curve Dynamics and Non-Price Determinants

  • Change in Quantity Demanded versus Change in Demand:

    • Change in Quantity Demanded: Movement along an existing demand curve (up or down). It is driven exclusively by a change in the price of the good itself.
    • Change in Demand: A complete shift of the entire demand curve to the right (increase in demand) or to the left (decrease in demand). It is caused by non-price determinants and has nothing to do with price.

  • Non-Price Determinants of Demand:

    • Income
    • Consumer tastes and preferences
    • Price of related goods (complements and substitutes)
    • Number of buyers in the market
    • Future expectations
    • Advertising and marketing

  • Real-World Advertisement Analysis:

    • Tom Brady Watch Advertisement: Represents a change in demand. The advertisement does not list the price of the watch. Consumers purchase it due to preference/taste (liking Tom Brady or the visual design of the watch).
    • KFC Advertisement: Represents a change in quantity demanded. The core selling point is the explicit price of 99 cents99\,cents, featured prominently to encourage consumers to buy a higher quantity at a lower price point.

Practice Scenarios: Demand vs. Quantity Demanded

  • Milk Demand Scenarios:

    • Scenario 1: A new study shows that milk makes you smarter. This causes an increase in demand (demand curve shifts to the right) because consumer preference increases regardless of price.
    • Scenario 2: A study shows that milk causes baldness. This causes a decrease in demand (demand curve shifts to the left) due to negative preference changes regardless of price.

  • Evaluative Test Scenarios:

    • Scenario A: A computer manufacturer lowers its prices. Answer: Change in quantity demanded. Lowering price results in moving down the existing demand curve.
    • Scenario B: A volleyball maker convinces high schools to fund varsity volleyball teams. Answer: Change in demand. Schools need additional volleyballs to supply new teams, increasing demand independent of volleyball prices.
    • Scenario C: A freeze ruins the orange crop and orange juice prices rise, affecting the market for apple juice. Answer: Change in demand for apple juice. Apple juice and orange juice are substitutes (e.g., standard machine choices at a hotel breakfast buffet). Although the statement mentions a price change, it is the price of orange juice that rose, not apple juice. Consumers switch from orange juice to apple juice, shifting the apple juice demand curve to the right.

Fundamentals of Elasticity

  • Definition of Elasticity: A measure of how sensitive consumer purchasing behavior is to a change in price.

  • Three Core Categories of Elasticity:

    • Inelastic: Quantity demanded is not sensitive to a change in price. Consumers continue purchasing the product regardless of price fluctuations.
    • Elastic: Quantity demanded is highly sensitive to a change in price. Small price changes dramatically alter consumption.
    • Unit Elastic: Quantity demanded changes in exact, proportional sensitivity to a price change.

  • Numerical Elasticity Thresholds:

    • Inelastic Good: Elasticity Value<1\text{Inelastic Good: Elasticity Value} < 1
    • Elastic Good: Elasticity Value>1\text{Elastic Good: Elasticity Value} > 1
    • Unit Elastic Good: Elasticity Value=1\text{Unit Elastic Good: Elasticity Value} = 1

Mathematical Formula for Price Elasticity of Demand

  • Five-Step Calculation Process:

    • Step 1: Isolate the original and new quantity values.
    • Step 2: Calculate percentage change in quantity using the formula:         % Change in Quantity=Original Quantity−New QuantityOriginal Quantity×100\% \text{ Change in Quantity} = \frac{\text{Original Quantity} - \text{New Quantity}}{\text{Original Quantity}} \times 100
    • Step 3: Isolate the original and new price values.
    • Step 4: Calculate percentage change in price using the formula:         % Change in Price=Original Price−New PriceOriginal Price×100\% \text{ Change in Price} = \frac{\text{Original Price} - \text{New Price}}{\text{Original Price}} \times 100
    • Step 5: Divide the percentage change in quantity by the percentage change in price:         Price Elasticity of Demand=% Change in Quantity% Change in Price\text{Price Elasticity of Demand} = \frac{\% \text{ Change in Quantity}}{\% \text{ Change in Price}}

  • Absolute Value Rule:

    • If any intermediate or final calculation yields a negative number, drop the negative sign (take the absolute value). Retaining negative signs leads to incorrect evaluations.

  • Worked Problem Example (Joe's Barbershop):

    • Data: Week 1 charges $15\$15 per haircut and serves 3232 customers. Week 2 charges $18\$18 per haircut and serves 2626 customers.
    • Step 1 & 2 (Quantity):32−2632=632=0.1875\frac{32 - 26}{32} = \frac{6}{32} = 0.18750.1875×100=18.75%0.1875 \times 100 = 18.75\%
    • Step 3 & 4 (Price):15−1815=−315=−0.2→0.2\frac{15 - 18}{15} = \frac{-3}{15} = -0.2 \rightarrow 0.20.2×100=20%0.2 \times 100 = 20\%
    • Step 5 (Elasticity):Elasticity=18.7520=0.93\text{Elasticity} = \frac{18.75}{20} = 0.93
    • Interpretation: The elasticity coefficient 0.930.93 is less than 11, meaning demand for haircuts at this location is inelastic. Customers are non-sensitive to the price increase.
    • Revenue Comparison:
      • Week 1 Revenue: \15 \times 32 = \480480
      • Week 2 Revenue: \18 \times 26 = \468468

Qualitative Determinants of Elasticity

  • Evaluating Elasticity Without Math:
    • 1. Availability of Substitutes:
      • No Substitutes = Inelastic. Example: Gasoline for standard motor vehicles. Drivers must fill their tanks when empty regardless of price.
      • Substitutes Available = Elastic. Example: Starbucks coffee priced from $5\$5 to $8\$8 causes consumers to substitute with Dunkin' Donuts, gas station coffee, or home-brewed coffee.
    • 2. Necessity vs. Luxury:
      • Necessity = Inelastic. Example: Essential prescription medications following surgery (e.g., specific sinus infection prescriptions costing over $300\$300 or $1200\$1200 for a child with allergies must be purchased regardless of price).
      • Luxury = Elastic. Discretionary items drop sharply in consumption if prices rise.
    • 3. Degree of Personal Importance:
      • High Importance = Inelastic. Example: A senior year homecoming or prom dress, or bucket-list experiences like purchasing tickets to the Rose Bowl (e.g., Michigan vs. Alabama college football semifinal) despite recent heavy travel expenditures in London.
      • Low Importance = Elastic. Price changes dictate purchasing choices.
    • 4. Percentage of Income / Budget:
      • Small Percentage = Inelastic. Example: A $2\$2 cup of coffee doubling in price adds $10\$10 per week, causing minimal budget impact.
      • Large Percentage = Elastic. Example: A truck payment doubling forces consumers to seek alternative vehicle options.
    • 5. Time Horizon (Short-Term vs. Long-Term):
      • Short-Term = Inelastic. Immediate needs reduce price sensitivity (e.g., paying for Chick-fil-A breakfast doubling to $500\$500 for a football team on Friday due to immediate necessity).
      • Long-Term = Elastic. Consumers adjust behavior over time (e.g., buying fast food less frequently or choosing non-steak options for weekend grilling after noticing high steak prices).

Total Revenue and the Total Revenue Test

  • Total Revenue Formula:Total Revenue=Price×Quantity\text{Total Revenue} = \text{Price} \times \text{Quantity}

    • Example: Selling 300300 pizza slices at $1\$1 per slice generates $300\$300 in total revenue. Total revenue measures gross intake, not profit (production costs must still be deducted).

  • The Total Revenue Test Principles:

    • Inelastic Products:
      • Price Increase →\rightarrow Total Revenue Increases.
      • Price Decrease →\rightarrow Total Revenue Decreases.
      • Application: Gas stations do not engage in price wars because lowering prices on inelastic goods leads to lower overall revenue.
    • Elastic Products:
      • Price Increase →\rightarrow Total Revenue Decreases.
      • Price Decrease →\rightarrow Total Revenue Increases.

  • Fast Food vs. Casual Dining Industry Case Study:

    • Fast food products are elastic.
    • Chains (McDonald's, Wendy's, Taco Bell, Burger King) raised combo meal prices from historical norms of $3.99\$3.99 to $12\$12, $13\$13, or $15\$15.
    • Raising prices on elastic goods caused total revenue and customer volume to drop as consumers viewed prices as unreasonable.
    • Casual dining chains (Chili's, Applebee's) targeted fast food customers by advertising full sit-down meals for $1\$1 less than fast food combos. Lowering relative prices on elastic meals redirected consumer volume to casual dining, increasing their total revenue.

Questions and Classroom Interactions

  • Question: Why does the Tom Brady watch advertisement demonstrate a change in demand rather than quantity demanded?

    • Answer: The ad omits price entirely. Purchasing decisions are driven strictly by endorsement preference or aesthetic attraction to the watch.

  • Question: Why is a price reduction by a computer manufacturer classified as a change in quantity demanded?

    • Answer: Price is the variable being manipulated to move consumers along the existing demand curve.

  • Question: In the orange juice vs. apple juice scenario, why is apple juice evaluated as a change in demand even though the word "price" appears in the question?

    • Answer: The prompt mentions the price of orange juice, which is a substitute good. The price of apple juice itself was not altered, making it a shift in demand for apple juice.

  • Classroom Discussion on Elasticity Homework Assignment:

    • Prompt: How should students format the practice problems for elasticity?
    • Answer: Apply the 5-step elasticity formula to scenarios (a) and (b), always starting calculations with quantity numbers followed by price numbers.