MGU Social Science Series — Economics: Principles of Microeconomics and Macroeconomics
Part I: Foundations of Economic Thinking
Incentives · Margins · Tradeoffs · Consequences
Chapter 3 of 30
MGU Social Science Series  ·  Economics: Principles of Microeconomics and Macroeconomics  ·  Library Textbook Edition

Chapter 3:
Incentives, Marginal
Thinking, and Tradeoffs

Why people respond to costs and benefits, why decisions are made one unit at a time, and why every choice gives something up

■ Part I: Foundations of Economic Thinking ■

■ 9 Sections  •  Chapter 3 of 30 ■

Continues from Chapter 2  ·  Prepares students for Chapters 4 through 30

Chapter 3 — Front Matter

Purpose and Overview

Imagine you are deciding whether to study for an extra hour tonight. You think about what you might gain — a better understanding of the material, perhaps a higher grade on Friday's test. You also think about what you give up — relaxation, time with friends, or sleep. Something about that calculation shapes your decision.

Now imagine a city council debating whether to widen a highway. Engineers say it will reduce commuting time. Environmental groups say it will increase emissions. Residents near the highway worry about noise. The city's budget is limited. Every choice the council makes trades one thing for another.

In both cases, something is driving the decision. Costs and benefits are being weighed. Small changes at the margin matter. Competing goals pull in different directions. This chapter introduces three of the most powerful tools in economic reasoning: incentives, marginal thinking, and tradeoffs. Together, these tools help explain how individuals, businesses, and governments make choices — and why those choices sometimes produce outcomes nobody planned.

Opening Question

Think about a decision you made recently — what to eat, whether to take a shift, how long to spend on homework. What did you gain? What did you give up? Did you weigh the whole decision, or just whether to do "one more" of something? By the end of this chapter, you will have precise tools for answering those questions — and for spotting when a policy's good intentions might still produce a bad result.

9Sections
10Objectives
17Key Terms
27Chapters Ahead

Learning Objectives

  1. 1Define incentive and distinguish positive incentives from negative incentives.
  2. 2Distinguish explicit costs from implicit costs and explain why both matter for decision-making.
  3. 3Apply marginal thinking to explain why decisions are made one unit at a time rather than all-or-nothing.
  4. 4Use marginal benefit and marginal cost to determine the optimal level of an activity.
  5. 5Explain the sunk cost fallacy and apply the principle that sunk costs should not influence forward-looking decisions.
  6. 6Identify tradeoffs faced by individuals, firms, and governments, including the efficiency-equity tradeoff.
  7. 7Explain why policies and incentives can produce unintended consequences.
  8. 8Distinguish short-run effects from long-run effects and explain why the distinction matters for policy analysis.
  9. 9Identify how incentives operate in markets, schools, firms, and government.
  10. 10Apply incentive analysis and marginal reasoning to real-world economic and policy scenarios.
Chapter 3 — Contents

Sections at a Glance

Sections 3.1 – 3.3
Incentives and the Logic of the Margin
What Incentives Are · Costs and Benefits · Marginal Thinking
Section 3.1

What Incentives Are

An incentive is anything that influences a person's decision by affecting the costs or benefits of a choice. Incentives are everywhere. A sale sign in a store window is an incentive to buy. A speeding ticket is an incentive to slow down. A scholarship is an incentive to study. A tax on cigarettes is an incentive to smoke less. A bonus for hitting a sales target is an incentive to sell more.

Notice that incentives work by changing what something costs or what it is worth. They do not force behavior — they shift the calculation. Economists often say people respond to incentives. This does not mean people always respond the way policymakers expect, or that they respond only to money, or that they ignore ethics and community norms. It means that changing the costs and benefits of an action changes how people behave.

Key Terms — Section 3.1
Incentive
Anything that changes the costs or benefits of a decision, thereby influencing behavior.
Positive Incentive
An incentive that raises the benefit of an action, encouraging more of that behavior.
Negative Incentive
An incentive that raises the cost of an action, discouraging that behavior.
IncentiveTypeExpected Effect
Store clearance salePositiveEncourages more purchases
Speeding ticketNegativeDiscourages speeding
College scholarshipPositiveEncourages study and enrollment
Cigarette taxNegativeDiscourages smoking
Bonus for hitting a sales targetPositiveEncourages more sales effort
Example 3.1.1
Reading an incentive change
  • SituationA city raises its parking fine downtown from $20 to $75.
  • IncentiveThe cost of parking illegally has increased sharply.
  • TypeThis is a negative incentive — it raises the cost of an action.
  • Predicted effectFewer drivers park illegally; more use legal parking or alternative transportation.
  • Possible twistSome drivers may park farther away in residential streets instead, shifting — rather than eliminating — the problem.
Key takeaway: Incentives reliably shift behavior in a predictable direction, but exactly how people adjust is not always the outcome planners expect.
Incentives Need Information — and Are Not Only About Money

Incentives work through information: if people do not know about an incentive, or do not understand it, they cannot respond to it. A tax credit nobody knows exists will not change behavior. Incentives also interact with values, habits, peer expectations, and social norms — status, fairness, and reputation all shape behavior, even when no money is involved.

Practice 3.1Identifying Incentives
  1. Classify each as a positive or negative incentive: (a) a rebate for buying an electric car; (b) a late fee on a library book; (c) free shipping on orders over $50; (d) a tax on sugary drinks.
  2. Explain why a financial incentive that nobody knows about will not change behavior. Give an original example.
  3. Describe one incentive in your own life this week that was not about money. What behavior did it change?
Section 3.2

Costs and Benefits

Every decision involves costs and benefits. A benefit is anything of value gained from a decision — financial, practical, physical, emotional, or social. A cost is anything of value given up by a decision — financial, time-based, physical, or psychological. The goal of economic reasoning is not to eliminate costs, since every choice has some cost, but to think clearly about what is actually gained and actually given up.

Economists distinguish between two kinds of costs. An explicit cost involves a direct payment of money — tuition, rent, wages paid to workers. An implicit cost does not involve a direct payment but still represents value given up — for example, the salary a business owner forgoes by working in her own shop instead of working elsewhere. That forgone salary is real, even though no money changes hands.

Key Terms — Section 3.2
Benefit
The value gained from a decision or action.
Cost
The value given up by a decision or action.
Explicit Cost
A cost involving a direct payment, such as money spent on materials, wages, or rent.
Implicit Cost
A cost that does not involve a direct payment but represents value forgone, such as the salary given up by running your own business.
FeatureExplicit CostImplicit Cost
Direct payment?Yes — money changes handsNo — value is given up without a payment
Appears in accounting records?YesUsually not
ExampleRent paid for a storefrontSalary given up by running your own business
Easy to overlook?RarelyOften — which is why economic profit differs from accounting profit
Example 3.2.1
Explicit and implicit costs of running a food truck
  • SituationA chef quits a $52,000-a-year restaurant job to run her own food truck full time.
  • Explicit costsTruck lease, ingredients, fuel, permits — all direct payments she can see on a receipt.
  • Implicit costThe $52,000 salary she gave up by leaving her job — no payment changes hands, but the value is real.
  • Why it mattersIf her food truck earns $45,000 in accounting profit, she is still worse off than if she had kept her old job, once the implicit cost is counted.
Key takeaway: Comparing only explicit costs to revenue can make a decision look better than it really is.
Practice 3.2Costs and Benefits
  1. Classify each as explicit or implicit: (a) wages paid to employees; (b) the interest income an owner forgoes by investing personal savings in her own company instead of a bond; (c) rent paid on a warehouse; (d) the unpaid time a volunteer board member spends advising a nonprofit.
  2. Give one example of a benefit that is not financial. Explain what makes it valuable even though no money is involved.
  3. Why might two businesses with identical accounting profit actually differ in how good an investment they are?
Section 3.3

Marginal Thinking

The word marginal in economics means "at the edge" or "one more." Marginal thinking asks: what happens if I do one more unit of something? Most real decisions are not all-or-nothing. You don't choose between no sleep and infinite sleep — you choose how many more hours to sleep. You don't choose between earning no money and earning unlimited money — you choose whether to work one more shift this week.

This approach reveals something important: a decision that made sense at first might not make sense at the margin. A student who studied zero hours and added one hour gained a lot. A student already studying eight hours who adds a ninth hour might gain very little — and give up sleep instead.

Key Term — Section 3.3
Marginal Thinking
Reasoning about the costs and benefits of one additional unit of an action, rather than treating decisions as all-or-nothing choices.
Cup of Water ConsumedTotal Value So FarMarginal Value of This Cup
1st cupHighVery high — relieves real thirst
2nd cupHighHigh
3rd cupModerateModerate
10th cupLow additionVery low — thirst is already satisfied
Why Water Can Be Cheaper Than Diamonds

Water is far more necessary for life than diamonds, yet diamonds usually cost more. The paradox dissolves once you think at the margin: in most settings, water is abundant enough that one more cup has low marginal value, while diamonds are scarce enough that one more diamond has high marginal value. Prices reflect marginal value, not total value — the same logic explains why a restaurant charges little for a second slice of pie while a hotel charges a great deal for a second room: the marginal cost of producing each differs sharply.

Practice 3.3Thinking at the Margin
  1. Explain in your own words why the value of "one more unit" can be very different from the value of the first unit.
  2. Use marginal thinking to explain why a person might eat a third slice of pizza eagerly but feel reluctant about a sixth slice.
  3. Give an original example, different from water and diamonds, where total value and marginal value point to different conclusions.
Sections 3.4 – 3.6
Optimizing at the Margin
Marginal Benefit and Cost · Sunk Costs · Tradeoffs Between Goals
Section 3.4

Marginal Benefit and Marginal Cost

The formal tools of marginal analysis are marginal benefit (MB) — the additional benefit received from one more unit of something — and marginal cost (MC) — the additional cost incurred from one more unit. Together they generate one of the most widely applicable rules in economics.

Key Terms — Section 3.4
Marginal Benefit (MB)
The additional benefit gained from one more unit of an activity.
Marginal Cost (MC)
The additional cost incurred from one more unit of an activity.
The Decision Rule

Do more of an activity if MB > MC. Do less if MC > MB. The optimal amount is where MB = MC (or as close as possible).

This rule applies to a firm deciding how many units to produce, a student deciding how many hours to study, a city deciding how many police officers to hire, or a government deciding how much to spend on road maintenance. In each case, the question is the same: does the next unit add more value than it costs?

Hours of ReviewMarginal BenefitMarginal Cost
1st hourVery highLow
2nd hourHighLow
3rd hourModerateModerate
4th hourLowHigh
5th hourVery lowVery high
Example 3.4.1
How many hours should the student study?
  • PatternMarginal benefit starts very high and steadily falls; marginal cost starts low and steadily rises, as shown in the table above.
  • Decision ruleKeep studying as long as MB exceeds MC.
  • ConclusionStopping around the 3rd or 4th hour likely makes sense; studying the 5th hour would cost more than it gains.
  • What this does not sayIt does not say studying is bad, or that the student should study zero hours — only that the additional hour must justify its additional cost.
Key takeaway: The optimal amount of an activity is found by comparing the next unit's benefit to its cost — not by maximizing or minimizing the activity altogether.
Practice 3.4Marginal Benefit and Marginal Cost
  1. A food truck owner sells 50 tacos a day. The 51st taco sells for $4 and costs $1.50 to produce. Should she make it?
  2. A farmer's 6th bag of fertilizer increases yield by $40 but costs $65. Should the farmer add it?
  3. A city's 101st sanitation worker would generate $6,000 in avoided health costs but costs $55,000 in salary. Should the city hire this worker?
  4. Explain why marginal cost and average cost are different ideas, even though students often confuse them.
Section 3.5

Sunk Costs and Why They Should Not Control Decisions

A sunk cost is a cost that has already been paid and cannot be recovered, regardless of what decision is made now — money already spent on a concert ticket you can no longer attend, tuition already paid for a class you are deciding whether to drop, research costs already spent on a product that isn't working. The economic principle is clear: sunk costs should not influence future decisions. Only current and future costs and benefits should matter.

This is harder than it sounds. People often continue investing in something simply because they have already invested in it — even when stopping would be the better choice. This is called the sunk cost fallacy.

Key Terms — Section 3.5
Sunk Cost
A cost already incurred that cannot be recovered, regardless of future choices.
Sunk Cost Fallacy
The mistake of letting previously incurred, unrecoverable costs influence current decisions.
SituationSunk CostForward-Looking Question
A struggling relationshipYears already invested togetherDoes staying produce more benefit than cost going forward?
A failing businessMoney already investedWill continued investment pay off from this point forward?
A disappointing movieTicket price already paidIs finishing the movie itself worth the remaining time?
An escalating commitmentResources already committedDo future costs outweigh future benefits of continuing?
Example 3.5.1
Applying the sunk cost principle to a product launch
  • SituationA company has spent $2 million developing a product. New market research shows the product will likely lose money if launched.
  • Sunk costThe $2 million is gone whether or not the product launches.
  • Relevant questionWill launching produce more benefit than cost going forward?
  • ConclusionIf the answer is no, the right decision is to stop — even though that feels painful after such a large investment.
Key takeaway: One of the most psychologically difficult principles in economics is also one of the most important for sound decision-making.
Common Misconception

"If I've already paid for something, I should use it to get my money's worth." This is the sunk cost fallacy. Once money is spent and unrecoverable, it should not determine future decisions — only your current and future wellbeing should matter.

Practice 3.5Sunk Costs
  1. A student has spent three months on a research paper that isn't coming together. Advisors say starting fresh would be more productive. Apply the sunk cost principle to this situation.
  2. Explain why "I've already paid for it" is not, by itself, a good reason to finish something.
  3. Describe a sunk cost fallacy you have witnessed or experienced. What would the economically sound decision have looked like?
Section 3.6

Tradeoffs Between Goals

A tradeoff occurs when getting more of one thing requires giving up some of another. Tradeoffs are unavoidable because resources — time, money, attention, land, energy — are limited. Using a resource for one purpose means it is unavailable for another. Tradeoffs appear at every level of decision-making.

Key Terms — Section 3.6
Tradeoff
A situation in which getting more of one good, goal, or outcome requires accepting less of another.
Efficiency
Using resources to produce the maximum possible value, with minimal waste.
Equity
Fairness in how costs and benefits are distributed among people.
Decision-MakerExample Tradeoff
IndividualSpending more time studying means less time working or resting
FirmHiring more workers raises output but also raises costs
GovernmentSpending more on roads means spending less on schools — or raising taxes
The Efficiency-Equity Tradeoff

One of the most important and recurring tradeoffs in public policy is between efficiency and equity. A tax system that funds extensive redistribution may reduce some efficiency incentives. A market that maximizes total output might not distribute that output in ways most people consider fair. Recognizing this tradeoff does not tell us which goal to prioritize — that is a normative question — but it is essential for honest policy analysis.

Practice 3.6Tradeoff Analysis
  1. A student chooses an unpaid internship over a paid service-industry job for the summer. What is being traded off?
  2. A government increases military spending without raising taxes. Identify the tradeoff.
  3. A farmer uses an acre of land to grow corn instead of wheat. What is the opportunity cost?
  4. Extended Question: A small town has a $500,000 budget surplus and must choose only one of: (a) repave 12 miles of road, (b) expand the public library, or (c) build a youth recreation center. What are the opportunity costs of choosing (a)? What tradeoffs must the council weigh? Why is there no single "right" answer?
Sections 3.7 – 3.9
Consequences, Time, and Incentive Design in Practice
Unintended Consequences · Short Run and Long Run · Incentives Across Institutions
Section 3.7

Intended and Unintended Consequences

One of the most important lessons of economics is that incentives and policies often produce unintended consequences — outcomes that weren't planned and sometimes weren't wanted. These occur because incentive effects are complex, people adapt to new rules in ways nobody predicted, economic systems are interconnected, and policymakers rarely know everything about how people will respond.

Key Term — Section 3.7
Unintended Consequences
Outcomes of a decision or policy that were not anticipated or intended, sometimes including effects opposite to those intended.
Example 3.7.1
The cobra effect
  • PolicyIn colonial India, the government paid a bounty for dead cobras to reduce the snake population.
  • Incentive createdPeople could earn money by killing cobras — but also by breeding them.
  • ResponseEntrepreneurial residents began breeding cobras specifically to collect the bounty.
  • OutcomeWhen the government ended the program, breeders released their now-worthless captive snakes, increasing the cobra population beyond its original level.
Key takeaway: A policy can change incentives in ways that work directly against its stated goal.
A Recurring Real-World Pattern: Rent Control

A city caps rents to make housing affordable. Landlords, facing lower returns, reduce maintenance and convert rental units to condos. The supply of rental housing falls, and long-run availability of affordable housing may worsen even as short-run rents are held down.

Not Every Unintended Effect Reverses the Goal

Some research has found that seat belt laws slightly increase risky driving, because drivers feel safer and may drive faster. The net safety effect is still positive — the unintended behavioral response only modifies the size of the benefit, rather than eliminating it.

Practice 3.7Unintended Consequences
  1. A state offers a $1,000 tax credit for installing solar panels. Identify the incentive, the expected behavior change, and one possible unintended consequence.
  2. A school district ties teacher bonuses entirely to standardized test scores. What unintended consequence might result?
  3. Explain, using the cobra effect, why good intentions are not sufficient for good outcomes.
Section 3.8

Short-Run and Long-Run Effects

Decisions and policies often have very different effects depending on the time horizon. The short run is the period in which some things are fixed and cannot easily change. The long run is the period long enough for all relevant adjustments to occur — firms can enter or exit markets, workers can retrain, consumers can change habits. These are not specific lengths of clock time; the distinction is about what can and cannot change, not a fixed number of months.

Key Terms — Section 3.8
Short Run
A period during which some inputs or conditions are fixed and cannot change.
Long Run
A period long enough for all inputs and conditions to fully adjust.
PolicyShort-Run EffectLong-Run Effect
Gasoline taxSmall change in driving — same cars, same homesDifferent vehicles, relocation, more transit funding
Minimum wage increaseLimited ability for firms to change business modelsMore options to automate, relocate, or restructure
A Standard Question for Sound Analysis

Sound economic analysis always asks: what are the short-run effects? What are the long-run effects? Do they point in the same direction? A policy that looks successful after one year may look very different after ten.

Practice 3.8Short Run and Long Run
  1. Explain why the short run and long run are defined by what can change, not by a fixed amount of time.
  2. Choose a policy or price change. Describe one likely short-run effect and one likely long-run effect.
  3. Why might policymakers be tempted to judge a policy only by its short-run effects? What risk does this create?
Section 3.9

Incentives in Markets, Schools, Firms, and Government

Incentive analysis is not just an abstract exercise — it shows up in every domain of economic and social life. In competitive markets, prices are the primary incentive mechanism: high prices attract producers, low prices push them toward other activities, and price signals coordinate decisions among millions of people without central direction. When prices are distorted by caps, floors, or subsidies, incentive effects change — sometimes unexpectedly.

DomainPrimary Incentive MechanismExample Effect
MarketsPricesHigh prices attract producers; low prices push them toward other activities
SchoolsGrades, funding formulas, tenurePerformance pay tied to test scores can narrow what is taught
FirmsWages, commissions, profit-sharingPiece-rate pay rewards effort but may sacrifice quality
GovernmentTax codes, regulation, reelectionPoliticians may favor short-term visible benefits over long-term, less-visible costs
The Economist's Constant Instinct

In all of these domains, the economist's instinct is the same: identify the incentives, then ask how people will respond to them — including responses that might not have been intended.

Practice 3.9Incentives Across Institutions
  1. A company pays its salespeople entirely on commission. Identify the incentive, the expected behavior change, and one possible unintended consequence.
  2. Explain how price caps can distort the incentive role that prices normally play in a market.
  3. Choose one domain from the table — markets, schools, firms, or government — and describe an incentive you have personally observed there.
Chapter 3 — Back Matter

Chapter Summary

Key Terms Review

incentive
Anything that changes the costs or benefits of a decision, thereby influencing behavior.
positive incentive
An incentive that raises the benefit of an action, encouraging more of that behavior.
negative incentive
An incentive that raises the cost of an action, discouraging that behavior.
benefit
The value gained from a decision or action.
cost
The value given up by a decision or action.
explicit cost
A cost involving a direct payment, such as money spent on materials, wages, or rent.
implicit cost
A cost that does not involve a direct payment but represents value forgone, such as a salary given up to run your own business.
marginal thinking
Reasoning about the costs and benefits of one additional unit of an action, rather than treating decisions as all-or-nothing.
marginal benefit (MB)
The additional benefit gained from one more unit of an activity.
marginal cost (MC)
The additional cost incurred from one more unit of an activity.
sunk cost
A cost already incurred that cannot be recovered, regardless of future choices.
sunk cost fallacy
The mistake of letting unrecoverable past costs influence current decisions.
tradeoff
A situation in which getting more of one thing requires accepting less of another.
efficiency
Using resources to produce the maximum possible value, with minimal waste.
equity
Fairness in how costs and benefits are distributed among people.
unintended consequences
Outcomes of a decision or policy that were not anticipated or intended.
short run / long run
The short run is a period when some inputs are fixed; the long run is long enough for all inputs and conditions to fully adjust.

Marginal Thinking Practice

For each scenario, identify the marginal benefit and marginal cost, then state whether the person should do the additional unit of the activity.

  1. A food truck owner sells 50 tacos a day. The 51st sells for $4 and costs $1.50 to produce. Should she make it?
  2. A student who has studied 4 hours estimates a 5th hour would raise his score by about 2 points, but he values the lost hour of sleep at about 4 score-equivalent points. Should he study the 5th hour?
  3. A city's 101st sanitation worker would generate $6,000 in avoided health costs but costs $55,000 in salary and benefits. Should the city hire this worker?
  4. A farmer's 6th bag of fertilizer per acre raises yield by $40 but costs $65 to buy and apply. Should the farmer add it?

Incentive Scenario Questions

For each scenario, identify (a) what incentive exists, (b) how it is expected to change behavior, and (c) any possible unintended consequences.

  1. A state government offers a $1,000 tax credit to homeowners who install solar panels.
  2. A company pays its salespeople entirely on commission — 10% of every sale.
  3. A school district ties teacher bonuses entirely to standardized test performance.
  4. A city imposes a $0.10 fee on plastic shopping bags at checkout.
  5. A health insurance company requires a $30 copay for every doctor visit.
  6. A factory faces fines for exceeding pollution limits but not for pollution below the limit.

Tradeoff Analysis

Identify the tradeoff in each situation and explain what is given up.

  1. A student takes an unpaid internship for the summer instead of a paid service-industry job.
  2. A government increases military spending without raising taxes.
  3. A farmer uses an acre of land to grow corn instead of wheat.
  4. A city builds a new highway through a neighborhood to reduce traffic congestion.
  5. A company switches to cheaper packaging materials to reduce costs.
Extended Question

A small town has a $500,000 annual budget surplus. Three proposals are on the table: (a) repave 12 miles of deteriorating roads, (b) expand the public library and add weekend hours, or (c) create a new youth recreation center. The town can only afford one. What are the opportunity costs of choosing option (a)? What tradeoffs must the town council weigh? Is there a "right" answer — and why is this partly a normative question?

Common Misconceptions

Misconception 1

"Incentives only work if they involve money." Incentives affect any cost or benefit people care about — not just money. Social recognition, status, peer pressure, fear of punishment, and personal satisfaction all function as incentives.

Misconception 2

"If I've already paid for something, I should use it to get my money's worth." This is the sunk cost fallacy. Once money is spent and unrecoverable, only current and future costs and benefits should guide the decision.

Misconception 3

"Tradeoffs only exist when someone makes a bad decision." Tradeoffs exist because resources are scarce, even when decisions are made perfectly. They are a feature of scarcity, not a sign of error.

Misconception 4

"If a policy has good intentions, it will produce good outcomes." Unintended consequences are common. Good intentions are not sufficient — careful analysis of likely incentive effects is essential for sound policy design.

Misconception 5

"Marginal cost and average cost are the same thing." Average cost is total cost divided by units produced; marginal cost is the cost of the next unit. A firm can have low average cost but high marginal cost near capacity.

Review Questions

Vocabulary in Context

  1. Define incentive and give one example of a positive incentive and one example of a negative incentive from daily life.
  2. What is the difference between an explicit cost and an implicit cost? Give one example of each.
  3. Explain what economists mean by the "short run" and the "long run." Why does the distinction matter for policy analysis?
  4. What is the sunk cost fallacy? Why is it considered an error in reasoning?

Concept Application

  1. A clothing store is deciding whether to hold a one-day clearance sale. Explain how a store manager could use marginal thinking to decide whether the sale is worthwhile.
  2. A local government raises the fine for jaywalking from $10 to $75. Using incentive analysis, explain the likely effect — and identify a potential unintended consequence.
  3. Explain the efficiency-equity tradeoff using a policy example of your choice. What does the policy gain in one dimension, and give up in the other?

Analysis Questions

  1. A student has spent three months on a research paper that is not coming together, and advisors suggest a new topic would be more productive. The student says, "But I've already put in all that time." Apply the sunk cost principle.
  2. A city hires traffic enforcement officers. Each additional officer reduces accidents by less than the one before. Using marginal analysis, at what point should the city stop hiring?
  3. A restaurant introduces a loyalty card: every 10th meal is free. Explain the incentive this creates for customers, then identify one possible unintended consequence for the restaurant.

Chapter 3 Checkpoint

Chapter 3 Checkpoint
Incentives, Marginal Thinking, and Tradeoffs — complete without assistance; assesses all key skills and concepts from Chapter 3
Section 1 — Vocabulary and Concepts
  1. Define "incentive" as used in this chapter. Why is it broader than "anything involving money"?
  2. Explain the difference between an explicit cost and an implicit cost, using an example of your own.
  3. State the sunk cost principle in one sentence. Why do people violate it so often in practice?
  4. Explain the difference between the short run and the long run, and why the distinction is about adjustment, not clock time.
Section 2 — Marginal Analysis
  1. A bakery's 30th loaf of bread costs $2.10 to bake and sells for $3.50. Its 65th loaf of the day costs $4.40 to bake (due to overtime labor) and still sells for $3.50. Should the bakery bake the 30th loaf? Should it bake the 65th? Explain using MB and MC.
  2. A city's first 10 streetlights each prevent several nighttime accidents. By the 40th streetlight on the same block, additional lights barely change accident rates. Explain, using marginal thinking, why the city should not use the same standard to evaluate the 5th and the 40th streetlight.
Section 3 — Analysis
  1. Describe a real or plausible policy that could produce an unintended consequence resembling the cobra effect. Identify the incentive it creates and the likely unplanned response.
  2. A classmate says, "If a tradeoff exists, someone must have made a poor decision." Correct this claim using concepts from the chapter.
Section 4 — Applied Practice
  1. Identify a decision you are currently facing or recently made. Describe: (a) the marginal benefit and marginal cost of "one more unit"; (b) any sunk costs that might tempt you to decide unwisely; (c) the tradeoff involved; (d) one incentive shaping your choice.
  2. Choose a real public policy. Identify its short-run effect, its likely long-run effect, and one possible unintended consequence. Explain whether the short-run and long-run effects point in the same direction.
Looking Ahead
Chapter 4: Economic Systems, Institutions, and Property Rights

Chapter 3 showed that incentives shape behavior and that choices involve tradeoffs and consequences. But incentives do not operate in empty space — they operate within rules, systems, and institutions that define what people can own, what contracts are enforceable, and how conflicts are resolved. Chapter 4 asks: what rules govern economic life? How do different societies organize production and distribution? What role do property rights, contracts, and rule of law play in shaping economic outcomes? Why do economies with similar natural resources sometimes produce such different results? Understanding institutions is essential for understanding why markets work well in some settings and poorly in others — and for thinking seriously about the role of government in the economy.

MGU Library Connection
  • Economics Reasoning Reference — Appendix B of this textbook
  • Chapter 4: Economic Systems, Institutions, and Property Rights — continues directly from Section 3.9
  • Chapter 8: Market Equilibrium — develops price signals and incentive effects of price ceilings and floors
  • Chapter 11: Production, Costs, and Profit — develops marginal cost and marginal revenue in full
  • Chapter 17: Information Problems and Behavioral Economics — extends incentive analysis to bounded rationality and nudges
  • Chapter 18: Government, Taxes, Regulation, and Redistribution — develops the efficiency-equity tradeoff in policy detail
  • MGU Dictionary entries: incentive, marginal benefit, marginal cost, sunk cost, tradeoff, efficiency, equity