Buffet Economics: Starting with Watermelon in the Dining Hall

There is one food at the Marian University dining hall that seems to obey its own law of supply and demand: watermelon.

When watermelon appears, people take it. Quickly.

I have watched a full tray shrink into half a tray, then a few scattered pieces, and finally almost nothing. What interests me is what happens near the end. By then, the remaining pieces do not always look especially fresh. Yet somebody still takes them.

There seems to be a small collective determination not to leave watermelon behind.

For a while, I assumed the explanation was simple: Americans really like watermelon.

Then I thought about shrimp.

The shrimp at the Chinese buffet

Anyone who has spent enough time at an all-you-can-eat Chinese buffet knows another familiar scene. A fresh tray of shrimp arrives. Suddenly people who had been peacefully wandering among noodles, broccoli, fried rice, and chicken become extremely attentive.

The shrimp disappear.

There is an obvious economic explanation. Shrimp feels expensive.

Rice does not. Potatoes do not. Bread certainly does not. If you paid $20 for a buffet, eating three plates of fried rice does not feel like a victory. A plate containing a suspicious amount of shrimp might.

Economists have actually studied this kind of behavior. An all-you-can-eat buffet is an unusual market because the customer pays a fixed entry price and then faces a marginal price of zero for the next bite. In theory, the money is already spent. Whether you eat two shrimp or twenty will not change the bill.

But people do not necessarily behave as though the price has disappeared.

Researchers have examined whether diners try to “get their money’s worth” after paying a buffet entry price. The evidence is not perfectly simple. Siniver and Yaniv, for example, modeled this motive explicitly and found that a higher entry price does not automatically make people eat beyond fullness. A later controlled study by Zuraikat and colleagues likewise found that doubling the stated cost of a meal from $8 to $16 did not significantly increase how much participants ate. In other words, “I paid more, therefore I must eat more” is not some universal law of human behavior. (De Gruyter Brill)

Still, the idea of getting value from a fixed-price meal is real enough to be recognizable. And the shrimp makes intuitive sense. If everything after admission costs zero, why fill scarce stomach space with foods you could buy cheaply anywhere?

So perhaps the buffet does not eliminate economic calculation.

It relocates it.

But that does not explain the watermelon

This is where the watermelon matters.

Nobody at Marian is loading up on watermelon because watermelon is the filet mignon of fruits. Nobody is doing mental arithmetic and concluding that six slices will finally defeat the university meal plan.

The shrimp explanation cannot simply be pasted onto the watermelon.

That would confuse two different kinds of value.

Shrimp can have monetary value: it feels expensive, indulgent, and worth selecting when the price of an additional serving is zero.

Watermelon has something closer to situational value.

It is cold. It is sweet. It contains a lot of water. It is easy to eat. Compared with many heavier dining-hall foods, it feels refreshing rather than demanding. You can put three pieces on a plate without making a commitment to another course.

And then there is scarcity.

Once a tray begins to empty, the calculation changes again. There may be more watermelon later. There may not. The last few pieces are objectively less attractive than the first few pieces, but they are also the last few pieces.

Psychologists and consumer researchers have long found that limited availability can increase perceived value. Michael Lynn’s review of the scarcity literature found broad support for the basic idea that things can become more desirable when they are harder to obtain. That does not prove that scarcity is causing the Marian watermelon phenomenon. My lunch observations are not an experiment. But it gives us a plausible reason why an almost-empty tray can generate its own momentum. (Wiley Online Library)

There is another possibility: we watch one another.

A 2021 observational study in a real self-service canteen followed 546 diners and found that people were more likely to select certain foods when the person immediately ahead of them had selected the same category. Food choice, like many other choices, is partly social. A busy tray can advertise itself. If everybody seems to be taking the watermelon, perhaps watermelon starts looking like the thing one is supposed to take. (PubMed)

The effect can then feed itself.

People take watermelon because they like watermelon.

The tray gets emptier.

The empty tray signals that other people like watermelon.

Now the watermelon looks both popular and temporary.

More people take watermelon.

Eventually someone takes the last slightly tired piece.

What are we maximizing?

This is what I find interesting about buffets.

Once the price of the next serving falls to zero, choice does not become meaningless. If anything, it becomes more revealing.

We still rank things.

We rank them by money: Shrimp is expensive.

By pleasure: Watermelon sounds good right now.

By convenience: I can eat two pieces without thinking about it.

By scarcity: There are only four left.

By social information: Everybody else seems to be taking this.

And probably by ten other things that never become conscious enough to put into words.

So “all you can eat” does not mean “all food becomes equal.” Removing the price of the next bite only removes one way of measuring value. We immediately invent others.

That may be the small economics lesson hiding inside the buffet line.

At the Chinese buffet, value sometimes looks like shrimp.

At my university dining hall, it sometimes looks like watermelon.

And if there is only one piece left, apparently it does not even have to be very good watermelon.

References

Garcia, A., Hammami, A., Mazellier, L., Lagneau, J., Darcel, N., Higgs, S., & Davidenko, O. (2021). Social modeling of food choices in real life conditions concerns specific food categories. Appetite, 162, 105162.

Lynn, M. (1991). Scarcity effects on value: A quantitative review of the commodity theory literature. Psychology & Marketing, 8(1), 43–57.

Siniver, E., & Yaniv, G. (2012). All-you-can-eat buffet: Entry price, the fat tax and meal cessation. The B.E. Journal of Economic Analysis & Policy, 12(1).

Zuraikat, F. M., Roe, L. S., Smethers, A. D., Reihart, L. W., & Rolls, B. J. (2018). Does the cost of a meal influence the portion size effect? Appetite, 127, 341–348.