Students can calculate elasticity perfectly and still miss the economic idea. To teach price elasticity of demand well, make price consequential. Students predict a quantity response, see revenue and inventory change, calculate elasticity, and then ask whether the comparison truly isolates movement along a demand curve.
A classroom market simulation adds exactly the complication that makes the lesson useful. Availability, differentiation, and competitor choices can also affect sales. Students learn the midpoint calculation, then learn when the evidence supports it and when it does not.
Begin with the definition and a prediction
Price elasticity of demand measures the responsiveness of quantity demanded to a change in price. Using absolute values, demand is elastic when the percentage change in quantity exceeds the percentage change in price, inelastic when it is smaller, and unit elastic when the changes are proportional.
Use the midpoint method so the calculated elasticity between two observations does not depend on which observation is labeled the starting point.
Midpoint price elasticity of demand = |[(Q2 – Q1) / ((Q1 + Q2) / 2)] / [(P2 – P1) / ((P1 + P2) / 2)]|
Before students enter a decision, ask each Team Company to predict whether demand will be relatively elastic or inelastic over its planned price change. They should state the expected quantity and total-revenue response.
Distinguish quantity demanded from units sold
The most important setup warning is that observed unit sales may be constrained. A company cannot sell more than it has available, even if customers would have demanded more. A stockout therefore prevents units sold from revealing unconstrained quantity demanded. Excess inventory does not prove demand was low for price alone. Competitors or product value may have mattered.
Define the variables shown by your simulation. If it reports unconstrained demand, use that for the cleanest elasticity estimate. If only units sold are visible, require students to check that neither comparison Round was capacity- or inventory-constrained. Mark estimates from constrained observations as lower bounds or unusable rather than pretending they are precise.
This distinction turns a familiar formula into good empirical practice. Students must validate the measurement before calculating.
Design a two-Round classroom comparison
In Round 1, ask Team Companies to choose a price near a common reference range and make sufficient production available. Do not require identical prices across teams. The market competition is part of the context. Have each team record price, predicted quantity, predicted revenue direction, and the condition that would invalidate its estimate.
After publishing Round 1, give teams their actual price, units sold or demand measure, inventory, Market Share, revenue, and relevant competitor evidence. In Round 2, ask them to change price by a deliberate but moderate amount while keeping production sufficient. They should hold other controllable demand investments constant where the scenario permits.
Absolute control is unlikely because competitors change simultaneously. Tell students that their first estimate is observational. They will later compare it with other companies and discuss the identification problem.
Calculate elasticity and the total-revenue test
After Round 2, students calculate midpoint elasticity from the two price and quantity observations. Require the full numerator and denominator, not only the final ratio. Then ask them to classify the response.
Use total revenue as a directional check.
- With elastic demand, a price decrease should increase total revenue, all else equal.
- With inelastic demand, a price decrease should reduce total revenue, all else equal.
- At unit elasticity, the opposing percentage changes offset.
If the calculation and revenue direction disagree, students should check capacity, inventory, market growth, competitor prices, and whether the quantity measure represents demand or fulfilled sales.
Do not let revenue become profit. A lower price may increase revenue while reducing contribution per unit or total profit. That distinction prepares the class for later pricing strategy.
Scroll sideways inside the graph and table to see all the data. You can also focus it and use the left and right arrow keys.
Start with two fictional observations where demand is fully served. Hold product value, marketing, rival behavior, and market conditions unchanged for this calculation. Price falls from $10 to $9 and quantity demanded rises from 100 to 140 units. These teaching assumptions create a cleaner comparison than a typical competitive Round.
| Observation | Unit price | Quantity demanded | Total revenue |
|---|---|---|---|
| A | $10 | 100 | $1,000 |
| B | $9 | 140 | $1,260 |
Quantity changes by 40 divided by 120, or 33.33%. Price changes by negative $1 divided by $9.50, or negative 10.53%. The absolute ratio is about 3.17, so demand is elastic over this interval. Revenue rises by $260. This calculation says nothing about profit without cost data.
Compare estimates across Team Companies
Create a table with each company’s price change, quantity change, estimated elasticity, stockout status, and major concurrent decision change. Remove estimates that fail the availability check. Then ask why the remaining estimates differ.
Possible reasons include different starting points on the demand curve, competitor responses, differences in Brand Index or Quality Index, and simultaneous marketing changes. If the scenario represents a closed competitive market, one company’s price can affect the demand served by others. The company-level elasticity students estimate is not automatically the market elasticity from a textbook demand schedule.
Use the simulation to teach ceteris paribus
Students often recite "all else equal" without treating it as a research condition. Ask them to list everything that failed to remain equal between the two observations. Sort the list into three columns.
| Own decision or state | Competitor or market change | Measurement constraint |
|---|---|---|
| Price, production, marketing, quality | Rival prices, market growth, demand conditions | Stockout, rounding, delayed effect |
Then ask which comparison would be more credible. They might select two Team Companies with similar availability and product value but different price changes, or use additional Rounds where demand investments remain stable. The goal is not to promise a perfect experiment. It is to make identification visible.
The Journal of Economics Teaching presents a physical activity that uses a bouncing ball to make the abstract price-quantity relationship visible. A simulation can extend that intuition by placing the relationship inside revenue, production, inventory, and competition decisions.
Address four common misconceptions
"Elastic demand means demand is high"
Elasticity measures responsiveness, not the level of demand. A company can face low demand that is highly responsive, or high demand that changes little with price.
"A steep demand curve is always inelastic"
Slope and elasticity are not identical because elasticity depends on percentage changes and the point on the curve. Keep the calculation tied to the observed price and quantity values.
"A lower price always increases revenue"
The revenue effect depends on elasticity. Even when revenue rises, profit may fall because unit margin is lower or costs change.
"Our two-Round result proves the causal elasticity"
It provides an estimate under stated assumptions. Simultaneous decisions, differentiation, and capacity can confound the comparison. Reward students for naming those limitations.
Debrief with evidence, mechanism, and limits
Use four questions.
- What price change did you make, and what quantity response did you predict?
- Was your company able to serve the demand it faced?
- What elasticity did you estimate, and did total revenue move in the expected direction?
- Which concurrent change most limits your interpretation?
Finish with a transfer question. "Would demand for the entire soda category be more or less elastic than demand for one Team Company’s soda, and why?" Students should discuss substitutes and market definition rather than guess a number.
For a written assessment, ask students to calculate the midpoint elasticity, classify it, perform the revenue check, identify one confounder, and propose a better next observation. Grade the reasoning and measurement choices as well as the arithmetic.
Run the lesson with Soda Market Intro
Soda Market Intro gives Principles of Microeconomics instructors a focused place to run this lesson in about 75 minutes. Team Companies begin with price and production. Marketing unlocks in Round 3 and R&D in Round 6, so you can establish price, demand, and inventory before differentiation adds another explanation.
The model provides explainable results, but a classroom comparison still reflects competitors and availability. Present the exercise as an estimate and debrief, not as a laboratory identification of one immutable elasticity coefficient.
The first 30 students in each Soda simulation are free. See Pricing for larger rosters, and use the one-session agenda to protect time for the calculation and limitation check. The formula is only the start. The evidence discussion is the lesson.
Frequently asked questions
How large should the price change be?
Use a change large enough to produce a visible response but still plausible within the scenario. Avoid extreme prices that trigger guardrails or make comparison with rivals less meaningful.
Can students calculate elasticity from Market Share?
Not as a substitute for quantity demanded. Market Share is a proportion of the market served and can change because the company, its rivals, or total market demand changed. Use a quantity measure and analyze Market Share separately.
Should marketing remain fixed?
Ideally, hold other demand-related decisions stable during the comparison. If the scenario or class behavior makes that impossible, record the changes and treat them as limits on interpretation.