Case Study 1 — Maya's Evening, Worked Through
Recall the scene from §1.1 of the chapter. Maya Diaz, a Millbrook State sophomore studying for tomorrow's macroeconomics exam, has just received a text from her shift manager at the Riverside Bistro: "Hey can you cover Sarah tonight 7-11? Need an answer in 5 min." It is 6:47 p.m. The exam is at 8 a.m. The shift would pay her about $80. Sarah is a friend who covered for Maya last month. The exam matters. So does the rent. So does the friendship. So does sleep.
This case study walks through Maya's decision the way an economist would — using the four ideas from Chapter 1. The point is not to give Maya the "right answer." There is no single right answer; the answer depends on details Maya knows that we don't (how prepared she is, how much she values the friendship, how stressed she is about rent, how sensitive her sleep is). The point is to show what it looks like to apply economic thinking to a real choice.
Step 1 — Identify the scarcity
What's scarce in Maya's situation?
The most obvious scarce resource is time. Maya has roughly five waking hours between now and bedtime, and she has more things she could profitably do with those hours than the hours can hold. She can't both work the four-hour bistro shift and do four hours of additional studying. The mathematical impossibility — five hours, two activities each demanding four — is the scarcity.
Less obvious but also scarce: energy. Even if Maya could somehow squeeze both activities in (working until 11 p.m., then trying to study until 3 a.m.), she wouldn't be able to absorb the studying effectively because she'd be exhausted. Mental energy is a real constraint, and it's one that economists sometimes underweight relative to time. (Behavioral economists, who pay more attention to actual cognitive limits, give energy more credit.)
Also scarce: information. Maya doesn't know exactly how prepared she is for the exam. She thinks she's reasonably prepared but not as prepared as she'd like. This uncertainty matters because it affects her marginal-benefit calculation in a way she can't fully resolve in five minutes.
The scarcity forces a choice. She can't do everything. She has to prioritize.
Step 2 — Identify the opportunity costs
For each option Maya is considering, what is the opportunity cost?
Option A: Take the shift, study less. - Opportunity cost: the additional studying she would have done. If she would have studied four more hours, the opportunity cost is four hours of exam preparation. The expected value of those four hours is some improvement in her exam grade — let's say a half-letter-grade improvement (from a B to a B+, or from a B+ to an A−), though Maya's actual estimate might be different. - Other costs: she's tired tomorrow, she's at work for four hours, she misses out on whatever else she might have done with the evening. - Benefits: $52 in wages plus tips (call it $80), the friendship credit with Sarah, the rent stress relief.
Option B: Decline the shift, study fully. - Opportunity cost: the $80 in wages, the friendship credit, and Sarah's awkward situation (she still has a covered shift to find). - Other costs: continued rent stress, the social cost of saying no. - Benefits: four more hours of preparation, better expected exam outcome, less day-of stress, some chance of moving up a letter grade.
Option C: Try to do both — take the shift, then study after. - Opportunity cost: sleep. Probably 4–5 hours of sleep. This is the most expensive option in non-obvious ways: studying while exhausted is barely studying, and being exhausted in the morning hurts the exam directly. - Benefits: feels like she's "doing everything" — but the analytical question is whether the benefits actually accrue.
The honest economic analysis of Option C is that it's almost always worse than it looks. The behavioral pull of "do both" is strong — humans hate giving things up — but the actual delivered value of "doing both" when sleep gets sacrificed is usually below the value of either option done well. We'll see this pattern again in Chapter 10's discussion of present bias and Chapter 17's discussion of capacity constraints.
So Maya's real choice is between Options A and B.
Step 3 — Apply marginal thinking
The all-or-nothing framing of Maya's choice obscures something important. The marginal question isn't "shift or no shift" — it's "for each additional hour I could choose to spend at the bistro instead of studying, is the marginal benefit of that hour at the bistro greater than the marginal benefit of that hour studying?"
For the first hour (7:00–8:00 p.m.): - At the bistro: she earns roughly $20 (with tips). She also helps Sarah. She uses an hour of her energy. - Studying: she gets some additional preparation. The marginal benefit of this hour depends on how much studying she's already done. If she's done two hours of solid review, the third hour is probably still pretty productive — she's covering material she hasn't yet covered. The marginal benefit is meaningful.
For the third hour (9:00–10:00 p.m.): - At the bistro: still earning, still helping Sarah, still using energy. - Studying: the marginal benefit is lower. She's been at it for a while; she's covering material she's already seen; she's getting tired. The graph in §1.3 of the textbook applies here — diminishing returns to studying past a certain point.
For the fourth hour (10:00–11:00 p.m.): - At the bistro: still earning, getting tired, but maybe handling drinks better than handling textbooks at this hour. - Studying: the marginal benefit is approaching zero or going negative. If she's been studying since the afternoon, hour 6 of cumulative studying is probably not improving her exam grade and might be hurting it (she's so tired tomorrow that she underperforms).
What does this analysis suggest?
If Maya has not yet done much studying tonight, the marginal value of additional studying is relatively high and the marginal value of working is relatively low. Decline the shift.
If Maya has already studied a lot today, the marginal value of additional studying is relatively low, the marginal value of working is steady, and the financial pressure tips the balance toward the shift. Take it.
If Maya is unsure how much studying she still needs (which is the realistic case), the question becomes how risk-averse she is about the exam. If the exam is a make-or-break grade for her course, she probably wants to err toward more studying. If the exam is one of many and her grade is already roughly secure, the financial reward is probably worth the marginal study cost.
Notice what this analysis is not doing. It is not telling Maya the "right answer." It is structuring the question so that Maya can answer it correctly given her own information. That's what economic thinking does. It doesn't decide for you. It clarifies what you're deciding.
Step 4 — Notice the incentives
What incentives are shaping Maya's situation?
- The bistro pays cash tips, which means the financial reward of working is visible and immediate. Tomorrow's exam grade is delayed and uncertain. Behavioral economists call this present bias: people systematically over-weight immediate rewards relative to delayed ones. Maya should be aware of this pull.
- Sarah's request is a social incentive. Returning a favor is part of how friendships work. Maya owes Sarah from last month, so saying no carries a real cost in the friendship account. This is also a real economic factor — relationships are resources, and burning them has costs.
- The exam is a structural incentive imposed by Maya's professor and her course. A higher grade in this class translates into a higher GPA, which translates into better job applications, which translates into long-run earnings. The benefit of studying is real but is several causal steps removed from tonight.
- The rent is a structural incentive imposed by Maya's landlord. If the rent is short, the cost is concrete and arrives at the end of the month. The closer to the end of the month Maya is, the more salient this incentive becomes.
Each of these incentives is doing real work in Maya's decision. None of them is morally objectionable. The question is which incentives Maya should weight most heavily — and the answer depends on her actual situation, not on a textbook.
Step 5 — What would I do?
I'm going to give you a real (if hedged) answer, because that's part of what makes a case study useful.
If I were Maya — knowing what we know — I would probably decline the shift. Three reasons.
First: the marginal value of an additional bistro shift, on a Tuesday in the middle of the semester with no specific financial crisis, is moderate. The marginal value of additional exam preparation, when the exam is tomorrow morning and Maya is "reasonably prepared but not as prepared as I want," is high. The opportunity cost of the shift is the difference between a B+ and an A−, or some similar grade jump, which probably matters more in the long run than a single $80 paycheck.
Second: doing both is a trap. Sleep deprivation will hurt Maya's exam performance directly, and trying to study at midnight after a four-hour shift is a particularly low-marginal-benefit activity.
Third: the friendship cost of saying no to Sarah is real but recoverable. Maya can text Sarah, explain that she has an exam tomorrow, and offer to cover one of Sarah's future shifts. If Sarah is a real friend, she will understand. The friendship is not destroyed by a single "I can't tonight." It might be slightly strained, and Maya should follow up on the favor she owes — but that follow-up can happen on a less consequential evening.
But — and this is important — I am not Maya. If Maya is barely making rent, if her grade is already locked in, if Sarah's emergency is severe enough to require this exact help, if Maya is actually well-prepared and is just second-guessing herself — any of these would change the calculation. The point of economic thinking is not to tell Maya what to do. It is to show her what she is choosing between, so that her decision is informed instead of impulsive.
Step 6 — What this case study reveals
Notice what we did. We didn't use any equations. We didn't draw any graphs. We didn't compute anything more elaborate than "more or less than." We applied four ideas — scarcity, opportunity cost, marginal thinking, incentives — to a normal-sized human problem, and we got a structured way to think about a decision that most people make on autopilot.
This is what the rest of the book is going to do, with progressively more sophisticated tools. The problems will get bigger (whole markets, whole economies). The tools will get more elaborate (supply curves, models of monetary policy, frameworks for thinking about climate). But the fundamental moves will stay the same. Identify what's scarce. Identify what's being given up. Think at the margin. Account for the incentives.
If you can do those four things consistently, you are already thinking like an economist — and you are already in better intellectual shape than most of the people who have opinions about economic policy without this framework.
Discussion questions
- Do you agree with my conclusion that Maya should probably decline the shift? What would change your mind?
- Have you been in a situation analogous to Maya's? How did you decide? Looking back, would you decide the same way now?
- The case study mentions "present bias" — the tendency to over-weight immediate rewards. Can you give an example of present bias in your own life?
- What would make this decision easier for Maya — more information, more time, a different financial situation, a different friendship dynamic? Which of those changes would matter most?
- Some people would argue that Maya should not have to make this choice at all — that a society in which a college student has to choose between exam preparation and rent money is failing in some basic way. Is that a positive claim, a normative claim, or both?