Essay two of four

The market for lemons

A used car market where the seller knows what the car is and the buyer does not. Set how far quality varies and how much of it a buyer can see, then watch the good cars leave one round at a time.

A hundred and twenty people each want to sell a car, and each knows exactly what their own is worth. Buyers know only that the cars in front of them lie somewhere in a range. Every car is worth half again as much to a buyer as to its owner, so under full information every one of them would sell.

Nobody in the model lies. Every seller accepts the offered price or keeps the car; every buyer offers what the cars on the lot are worth on average. From those two reasonable rules the market takes itself apart.

01The lot

Each mark is one car, from the worst on the left to the best on the right, with its quality on the vertical scale. Set the spread of quality and how much of it a buyer can see, then run the market. The line is the quality above which an owner would rather keep the car than take the price.

Figure one the cars, round by round

02Why it unravels

The loop has four steps and closes on itself. Buyers offer a price built on what they believe the average car is worth. At that price the owners of the best cars decline. The cars on offer are therefore worse than the cars available, so buyers revise the average down and offer less, which drives out the next layer of good cars.

Step through the rounds and watch the line come down. The two series are the average quality of the cars that changed hands in each round and the average price paid. They fall together, because the price is an estimate of the quality, and the estimate is chasing a quantity it is itself pushing down.

Figure two quality and price over the rounds

It does not always go to zero. If the worst car on the lot is still a decent car, the spiral runs out of room and the market settles smaller and worse than it should be, but alive. If the worst car is worthless there is no floor, and the market falls all the way through. Push the spread to its maximum to see that.

03The number that decides it

The whole spiral is one line of arithmetic. A buyer who sees a fraction of the quality and guesses the rest offers a price built from both; an owner sells when that offer is at least what the car is worth to them. Working the inequality through gives the highest quality still offered for sale.

highest quality still offered = 1.5 x (1 minus visibility) x believed average / (1 minus 1.5 x visibility) With no visibility at all the expression is just one and a half times the believed average. As visibility rises towards two thirds the denominator goes to zero and every car sells whatever the belief.

That threshold is why the visibility control has a point where the behaviour switches rather than a smooth slope. When the worst car is worthless, the market survives only if buyers can see more than a third of what they are buying. Below a third the whole thing goes to nothing; above it, it holds. Set the spread to its maximum and move visibility across a third.

04Two ways to put it back together

Nothing above required anybody to behave badly, so nothing above is fixed by asking people to behave better. What fixes it is changing what a buyer's money is exposed to. The remedy control offers two ways, and they work differently enough to try one after the other.

A certificate attacks the ignorance directly: an inspection reveals most of what the buyer could not see, for a fee. Switch it on and the line jumps above the top of the lot, since with quality visible nobody has a reason to withdraw. The fee comes out of what the seller receives, so the market that comes back is slightly smaller than the ideal one.

A warranty attacks the exposure instead: the seller promises to make good any shortfall against a stated standard, so the buyer pays for the standard rather than for a guess. The bad cars now sell, because their owners can carry the repair bill and still come out ahead. The very best cars withdraw, because a warranty pays the same for an excellent car as for an adequate one. The remedy rescues the market and truncates it at the top.

05What Akerlof actually wrote

The paper is George Akerlof's, thirteen pages in the Quarterly Journal of Economics, August 1970. The used car market is its opening illustration. The general claim is that where one side of a trade knows the quality and the other does not, the bad drives out the good, and the loss falls on the honest seller who can no longer prove that their car is good.

The model above is a numerical version of that argument. Akerlof's arithmetic is starker: buyers value cars at three halves of what owners do, quality is spread evenly from zero upward, and the only price consistent with itself is zero. The market does not shrink, it vanishes. The spread control reaches that case at its maximum.

The American Economic Review and the Review of Economic Studies both turned the paper down as too trivial, and a referee at the Journal of Political Economy objected that if it were correct then no goods could be traded at all. Thirty one years later Akerlof shared the 2001 economics prize with Michael Spence and Joseph Stiglitz for the analysis of markets with asymmetric information.

06Where the model stops

Assumptions and limits

One shot buyersEvery buyer arrives once, buys or does not, and leaves. No repeat customers, no reputation, no word of mouth, which in a real market are among the strongest forces holding quality up.
Beliefs update crudelyBuyers set this round's belief to last round's realised average. A fully rational buyer would jump straight to the fixed point, and there would be no spiral to watch. The rounds are a teaching device; the end point is the same either way.
Quality is one numberReal cars are good in some ways and bad in others. Compressing that into a single hidden scalar makes the picture drawable, and is the largest thing it leaves out.
The remedies are sketchesThe certificate is a jump in visibility with a flat fee; the warranty is a promise to make up any shortfall against a fixed standard, again with a flat fee. Real warranties are priced, limited, disputed and sometimes not honoured, and real certification schemes can be captured by the sellers who pay for them.
The warranty is a transferThe repair a warranty pays for is treated as money moving from seller to buyer; in the model it consumes no real resources. A treatment in which repairs consume resources would leave the market smaller than it appears here.
Nothing is estimatedThe multiplier of one and a half, the hundred and twenty cars, the fees and the fourteen rounds are chosen so that the mechanism is visible. None of them is measured from any real market.
Adverse selection is one reading among severalUsed cars sell below new cars for reasons that have nothing to do with hidden information, wear and depreciation among them. A market showing the pattern is no proof that this mechanism produced it.

07Sources

The paper itself, and the numerical example in which buyers value cars at three halves of the owner's valuation and quality is spread evenly, so that no price above zero is consistent with itself. George A. Akerlof, The Market for “Lemons”: Quality Uncertainty and the Market Mechanism, The Quarterly Journal of Economics, volume 84, number 3, August 1970, pages 488 to 500. DOI 10.2307/1879431. doi.org/10.2307/1879431 Bibliographic details confirmed at en.wikipedia.org/wiki/The_Market_for_Lemons. The setup, a buyer willing to pay three halves of the seller's valuation, quality distributed uniformly, and a unique equilibrium price of zero at which no car is sold, is set out in George Georgiadis, Information Economics, Module 14: Adverse Selection, Kellogg School of Management, kellogg.northwestern.edu/faculty/georgiadis/Teaching/Ec515_Module14.pdf. Checked 2026 08 21.
Akerlof's own account of the rejections: the American Economic Review and the Review of Economic Studies declined the paper on the ground that they did not publish work on subjects of such triviality, and a referee at the Journal of Political Economy held that if the paper were correct then no goods could be traded. George A. Akerlof, Writing the “The Market for ‘Lemons’”: A Personal and Interpretive Essay, published by the Nobel Foundation, 2001. nobelprize.org/prizes/economic-sciences/2001/akerlof/article Read through the summary at equitablegrowth.org. Checked 2026 08 21.
The 2001 Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel was awarded jointly to George A. Akerlof, A. Michael Spence and Joseph E. Stiglitz for their analyses of markets with asymmetric information. The Nobel Foundation, prize summary for 2001. nobelprize.org/prizes/economic-sciences/2001/summary Checked 2026 08 21.
Warranties, vehicle history reports, brand reputation and licensing are the institutions usually named as market answers to the problem, rather than statutory ones. David R. Henderson, editor, The Concise Encyclopedia of Economics, biography of George Akerlof, Library of Economics and Liberty. econlib.org/library/Enc/bios/Akerlof.html Checked 2026 08 21.