Product differentiation and entry

Paper packet. Every task here also exists on screen, where it is checked automatically; answers written on paper are not assessed by Nydus. When you are back at a device, enter your answers there.

1. What you will learn

Analyze product differentiation and entry using explicit assumptions, calculated results and a stated limit of the model.

2. Starting point

A seller facing downward-sloping demand has marginal revenue below price. Profit compares revenue with all opportunity costs. Entry can erode profit, but its effect depends on whether entrants sell identical products or differentiated substitutes.

3. Terms and units

4. Many sellers can still face downward demand

Monopolistic competition combines features that should not be collapsed into either perfect competition or monopoly. Many firms sell products that buyers regard as substitutes, but those products differ in some relevant way. Location, design, service, convenience or perceived identity can make a particular seller's product attractive to a subset of buyers. Each firm therefore faces a downward-sloping demand curve for its own variety rather than the perfectly horizontal line of the price-taking benchmark.

The word monopolistic does not mean that each seller controls an entire broad market without competition. Its limited market power concerns its differentiated variety, while other varieties constrain demand. A café can have some discretion over its own price because customers value its location or service, yet lose many customers if it charges too much relative to nearby alternatives. The strength of substitution affects the elasticity of its demand and the extent of its feasible markup.

The word competition refers partly to the presence of many alternatives and partly to entry and exit. New firms can introduce additional varieties when profit opportunities exist. That entry tends to reduce demand for each incumbent's variety and can make it more elastic as buyers gain alternatives. The long-run mechanism therefore differs from a monopoly protected by durable barriers. The relevant assumptions must be stated rather than inferred from a product's branding alone.

Differentiation can be real or perceived, and it is not necessarily wasteful. Buyers may value different locations, features or service levels. A welfare comparison must consider those benefits as well as costs and markups. The standard diagram isolates a firm's quantity and cost relationship; it does not measure every benefit of having a variety of products available. Labeling all differentiation an inefficiency would exceed what the diagram establishes.

Term	What it means
Monopolistic competition	A model with many sellers of differentiated substitutes and sufficiently free entry and exit.
Product differentiation	Features, location, service or perceived qualities that make products imperfect substitutes.
Markup	The difference between price and marginal cost, with a ratio used only when explicitly specified.
Long-run tangency	The model condition where a firm's demand curve touches ATC at its zero-economic-profit output.
Excess capacity	The gap between a firm's actual output and the output minimizing its average total cost in the standard long-run diagram.
Nonprice competition	Attempts to attract buyers through product characteristics, service, advertising or other dimensions besides the posted price.

Another way: The short-run calculation resembles monopoly

A differentiated seller chooses output by comparing marginal revenue with marginal cost, using the same logic as another downward-demand seller. It then reads the price from its demand curve at that quantity. Price is generally above marginal revenue for positive output under single pricing. Setting price equal to marginal cost would solve a different benchmark, not the firm's stated profit-maximization problem.

Suppose a firm chooses ten units at a demand price of fourteen dollars, where the relevant MR equals MC. Average variable cost at that output is eight dollars and fixed economic cost is forty. Average fixed cost is four and average total cost is twelve. The firm earns a two-dollar margin per unit and twenty dollars of economic profit. Revenue, variable cost and fixed cost can be assembled directly as a check: 140 minus 80 minus 40 equals 20.

If demand is weaker, the same kind of firm may earn a loss. The short-run shutdown comparison still asks whether operating covers avoidable variable cost at the best positive output. Product differentiation does not repeal that comparison. A firm with price below ATC but above the relevant AVC may operate temporarily while planning to exit if it cannot cover all opportunity costs in the long run.

The short-run picture should not be mistaken for a permanent equilibrium merely because MR and MC intersect. That condition selects the firm's current output given demand and cost. Positive economic profit can attract entry, and losses can induce exit. Those adjustments change the demand facing the individual variety. Long-run analysis therefore needs an additional condition about the incentive for firms to enter or leave.

Another way: Entry removes profit without removing the markup

When new varieties enter, buyers have more substitutes. Under the standard symmetric model, each incumbent's demand shifts inward and may become more elastic. Its optimal quantity and price change. Entry continues while opportunities for positive economic profit remain, subject to the assumptions about feasible comparable entrants. In long-run equilibrium, firms earn zero economic profit: price equals average total cost at the chosen output.

Because the individual demand curve still slopes downward, price can remain above marginal cost even though price equals ATC. There is no contradiction. Average total cost includes costs spread over all units, while marginal cost concerns the next unit. A markup over marginal cost can help finance fixed costs without leaving economic profit after all costs are covered. Zero profit therefore does not imply perfect competition or the disappearance of product differentiation.

In the conventional smooth diagram, the firm's demand curve is tangent to ATC at the long-run chosen output, while MR intersects MC at that quantity. The tangency means no feasible nearby price-output point on demand yields revenue above average total cost under the given curve configuration. Merely drawing demand crossing ATC at some arbitrary point is insufficient to establish the long-run profit-maximizing condition. Both the output rule and the no-entry-profit condition must be satisfied.

The long-run tangency typically occurs on the declining portion of ATC, to the left of its minimum. Actual output is then smaller than the quantity that would minimize average cost. The difference is called excess capacity. If actual output is ten and minimum ATC occurs at fourteen, excess capacity is four units. This is a comparison of quantities on the firm's cost diagram, not a statement that four physical machines necessarily stand idle or that the firm should produce unwanted units.

Another way: Interpret excess capacity and variety carefully

Excess capacity highlights a cost comparison: producing more of a given variety could reduce its average cost over the relevant range, but demand and the firm's pricing incentives do not support that output in the long-run differentiated equilibrium. It does not mean the firm can profitably sell the extra units at the current price. Expanding sales would require moving along its downward demand curve, changing revenue as well as cost.

The conventional diagram also shows price above marginal cost, indicating that an additional unit would be valued above its marginal production cost at the observed quantity. This resembles the static output distortion under monopoly. But comparing an entire differentiated industry with an identical-product benchmark requires more than adding individual triangles. A different number of varieties changes consumer choice and may change costs. The benefit of variety is not automatically captured by one firm's demand-and-cost diagram.

Advertising can provide information about existence, price or features, and it can also attempt to alter perceptions or brand loyalty. It uses resources, so its cost belongs in the analysis when relevant. Whether advertising raises or lowers welfare depends on its content, effect and cost. A model can specify an advertising expenditure that shifts demand and then calculate profit, but a higher profit alone does not establish a social gain. Consumers' information and choices must also be considered.

Quality and location are other forms of nonprice competition. Two firms may charge different prices because one provides a costly service improvement, not because the difference is pure market power. Conversely, perceived differentiation may support a markup even when physical production costs are similar. A careful comparison identifies the complete product and its cost rather than treating all nominal prices as payments for identical units.

The assumption of sufficiently free entry is essential to the zero-profit result. A valuable scarce location, protected design or durable brand advantage can restrict imitation and change the outcome. Firm heterogeneity can also generate different profits even while marginal entrants earn zero. The symmetric textbook equilibrium is a benchmark explaining an entry mechanism, not a claim that every café, shop or service provider earns exactly the same return.

For an answer within the benchmark, report the firm's MR-MC output, demand price, ATC, profit and excess-capacity comparison where supplied. Then identify what long-run entry is assumed to change. Keeping these entries separate avoids two common overstatements: that entry eliminates all market power, and that a markup guarantees positive economic profit. Both are contradicted by the model's long-run combination P = ATC with P greater than MC.

Another way: Differentiate the market definitions

A single firm demand curve describes one variety, while an industry demand curve groups substitutes under a broader market definition. Entry can reallocate purchases among varieties without increasing every incumbent sales. Before interpreting a shift, identify which market the curve describes and whether new varieties change the product grouping. This prevents a statement about increased industry participation from being mistaken for an outward shift of every incumbent demand curve.

5. A fictional differentiated studio after entry

An invented craft studio sells a distinctive workshop experience. Initially it chooses ten sessions at a price of fourteen dollars, where its marginal revenue equals marginal cost. AVC is eight dollars and fixed economic cost is forty. ATC is twelve, so economic profit is twenty dollars. Buyers have alternatives, but the studio's particular location and format give it downward-sloping demand rather than the horizontal demand of a perfect price taker.

New studios enter with other formats. In the supplied long-run diagram, the incumbent's demand shifts until it is tangent to ATC at ten sessions and a price of twelve dollars. Economic profit is now zero. The minimum of ATC occurs at fourteen sessions, so the diagram's excess capacity is four. The studio's marginal cost at the chosen point can remain below twelve; the markup helps cover costs that are not captured by the next session's marginal cost.

It would be wrong to advise producing fourteen sessions merely because that minimizes ATC. The studio cannot assume all fourteen will sell at the old price. It must consider its demand and the revenue consequences of expansion. It would also be wrong to call the additional varieties worthless merely because each studio operates below its minimum-cost scale. Participants may value differences in timing, location or content, benefits that need explicit consideration in an industry-wide welfare comparison.

The exercise gives exact numbers to make the distinctions visible. A real study would need evidence about substitution, entry barriers, costs and the value of variety. The bounded conclusion is that free entry can eliminate economic profit while leaving downward demand, a marginal-cost markup and excess capacity in the conventional model. It is not a claim that every differentiated market has the same desirable or undesirable features.

6. Check the tempting shortcut

Zero economic profit means P equals ATC, not necessarily MC. Entry can leave a markup and excess capacity. The minimum-ATC quantity is not automatically profitable to sell, and the cost diagram alone does not measure all benefits of product variety.

7. In the fictional Alder model, a differentiated seller initially chooses 9 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 36 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 9 and price 12, while minimum ATC occurs at quantity 13. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

8. In the fictional Birch model, a differentiated seller initially chooses 10 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 40 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 10 and price 12, while minimum ATC occurs at quantity 14. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

9. In the fictional Cedar model, a differentiated seller initially chooses 11 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 44 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 11 and price 12, while minimum ATC occurs at quantity 15. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

10. In the fictional Dune model, a differentiated seller initially chooses 12 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 48 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 12 and price 12, while minimum ATC occurs at quantity 16. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

11. Guided practice

In the fictional Elm model, a differentiated seller initially chooses 13 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 52 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 13 and price 12, while minimum ATC occurs at quantity 17. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

12. Guided practice

In the fictional Dune model, a differentiated seller initially chooses 12 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 48 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 12 and price 12, while minimum ATC occurs at quantity 16. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

13. Guided practice

In the fictional Fern model, a differentiated seller initially chooses 14 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 56 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 14 and price 12, while minimum ATC occurs at quantity 18. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

14. Practice

In the fictional Grove model, a differentiated seller initially chooses 15 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 60 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 15 and price 12, while minimum ATC occurs at quantity 19. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

15. Practice

In the fictional Harbor model, a differentiated seller initially chooses 16 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 64 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 16 and price 12, while minimum ATC occurs at quantity 20. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

16. Somewhere new

A distinctive workshop studio faces new rival formats. Its supplied diagram describes both the initial profit opportunity and the long-run demand tangency after entry. Keep the minimum-cost scale separate from the quantity the studio can profitably sell. In the fictional Island model, a differentiated seller initially chooses 17 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 68 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 17 and price 12, while minimum ATC occurs at quantity 21. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

17. Lesson test

Lesson test: one question per skill, one attempt each, no hints. Your answers are checked when you submit.

18. Test question

In the fictional Juniper model, a differentiated seller initially chooses 18 units, where MR=MC, at a demand-curve price of 14 dollars. AVC is 8 dollars and fixed cost is 72 dollars. Free entry later shifts each incumbent's demand until economic profit is zero. A supplied long-run diagram places the tangency at quantity 18 and price 12, while minimum ATC occurs at quantity 22. Calculate initial ATC, initial economic profit, and long-run excess capacity in units.

19. What you can do now

Reconstruct the model without the worked example. Explain each requested measure's units and identify an assumption that the conclusion depends on.

Working for the steps left to you

	Calculated value
Initial ATC
Initial economic profit
Excess capacity

	Calculated value
Initial ATC
Initial economic profit
Excess capacity

	Calculated value
Initial ATC
Initial economic profit
Excess capacity

	Calculated value
Initial ATC
Initial economic profit
Excess capacity