Price Discrimination vs Product Differentiation

The student discount test tells you which one a stem is describing

Ask one question about the buyer who pays more: does that buyer receive anything different? A cinema selling the identical seat at the identical showing for $9 to students and $14 to everyone else has changed only the price tag, so the practice is price discrimination. A software firm that ships a student edition with the collaboration tools stripped out has changed the product, so the same $5 gap is product differentiation, often called versioning. The border case worth knowing is airline pricing. Two passengers on one flight paid different fares, which looks like discrimination, but the cheaper ticket is usually non-refundable, booked earlier, and seated further back, which makes it a genuinely different product. A grader accepts either label on a case like that provided you name the thing that differs. What loses credit is answering that the firm charges more because its product is better on a stem that has already told you the good is identical.

Perfect discrimination erases deadweight loss, differentiation leaves excess capacity

Take a price setter facing P = 60 - Q with constant marginal cost of $20. Charging one price, it sets MR = 60 - 2Q equal to 20, sells 20 units at $40, and collects producer surplus of $400 while buyers keep $200. Output stops well short of the 40 units where price would equal marginal cost, and the deadweight loss triangle is $200. Now let the firm charge every buyer the most that buyer will pay. It sells all 40 units, total surplus rises from $600 to $800, deadweight loss falls to zero, and consumer surplus falls to zero as well. Efficiency improves while buyers lose everything, which is why the exam wants efficiency and equity discussed separately here. Product differentiation carries the opposite signature. In long-run monopolistic competition, entry drives economic profit to zero, average total cost sits tangent to a downward-sloping demand curve, and the firm produces to the left of minimum average total cost. Price still exceeds marginal cost, so the inefficiency stays, and no transfer of surplus removes it. Naming which inefficiency you mean is most of the point on a free-response part.

Differentiation supplies the market power that discrimination then spends

Three conditions make price discrimination possible: the firm must be a price setter, it must be able to sort buyers into groups with different elasticities of demand, and it must stop the cheap group reselling to the dear group. Differentiation is one common route to the first condition, which makes the two ideas sequential rather than interchangeable. A gym with a recognizable local brand faces a downward-sloping demand curve because of that brand, and it then spends the resulting market power by charging $30 to anyone who shows a student card and $45 to everyone else, with the same hours, the same equipment, and the same classes for both. Nothing about the product differs, so this is discrimination, and the photograph printed on the card is what blocks resale. Two rules sit inside that example. The lower price goes to the more elastic group, never the reverse, and the sorting device has to be something buyers cannot fake or trade. Notice the limit as well. A firm selling an undifferentiated bulk commodity that any buyer can resell within the hour cannot discriminate no matter how large it is, because arbitrage collapses the two prices into one. Market power is necessary and nowhere near sufficient, and resale is the condition students forget to mention.

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