AP Macroeconomics

## Learning Outcomes

- Distinguish clearly between a **change in demand** and a **change in quantity demanded**
- Identify the main non-price determinants that shift the demand curve
- Explain how income affects **normal goods** and **inferior goods** differently
- Apply substitute and complement logic to related-goods questions
- Predict how a rightward or leftward demand shift changes equilibrium price and quantity when supply is unchanged
- Use correct AP graph language for movements along curves versus shifts of curves

## AP Macroeconomics Syllabus

For the AP Macroeconomics, you are expected to understand demand determinants that shift the demand curve, with a focus on the following syllabus points:

- Know that a change in the good’s own price causes a **change in quantity demanded**, shown as movement along a demand curve
- Identify that non-price determinants cause a **change in demand**, shown as a shift of the entire demand curve
- Explain how **tastes/preferences**, **income**, **prices of related goods**, **expectations**, and **number of buyers** affect demand
- Understand the difference between **normal goods** and **inferior goods** when income changes
- Distinguish accurately between **substitutes** and **complements**
- Predict that, with supply held constant, an increase in demand raises equilibrium price and equilibrium quantity
- Predict that, with supply held constant, a decrease in demand lowers equilibrium price and equilibrium quantity
- Avoid confusing product-market demand in Unit 1 with **aggregate demand** later in macroeconomics

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What is the difference between a change in demand and a change in quantity demanded?
2. If the price of coffee rises, what happens to demand for tea if tea is a substitute?
3. How does a rise in income affect a normal good differently from an inferior good?
4. Why does an expectation of higher future prices often increase current demand?
5. If demand increases and supply stays the same, what happens to equilibrium price and equilibrium quantity?

## Introduction

In AP Macroeconomics Unit 1, demand begins with a simple but heavily tested idea: **price changes move you along a demand curve, while non-price changes shift the entire curve**. Many students know the words but lose points when they apply them in a graph or multiple-choice question.

This topic matters because it appears in basic market analysis, equilibrium questions, and graph interpretation. It also creates a foundation for later macro topics. If you confuse product demand with aggregate demand, or demand with quantity demanded, many later questions become harder than they need to be.

> **Key Term: demand**
> The relationship between the price of a good and the quantity consumers are willing and able to buy at each price.

### Change in quantity demanded versus change in demand

This is the most tested distinction in the whole topic.

A **change in quantity demanded** happens only when the good’s own price changes. Nothing shifts. You simply move to another point on the same demand curve.

If the price of movie tickets falls from $15 to $12, consumers buy more movie tickets. Economists do **not** say demand increased. They say **quantity demanded increased**. The curve stays fixed because the only thing that changed was the ticket price.

A **change in demand** happens when consumers want more or less of a good at every possible price. That means the whole curve shifts.

If a famous athlete promotes a certain brand of shoes, consumers may want more of those shoes whether the price is $80, $100, or $120. That is an increase in demand, so the demand curve shifts right.

> **Key Term: quantity demanded**
> The specific amount of a good consumers are willing and able to buy at a given price.
>
> **Key Term: change in quantity demanded**
> A movement along an existing demand curve caused only by a change in the good’s own price.
>
> **Key Term: change in demand**
> A shift of the entire demand curve caused by a non-price determinant of demand.

The graph logic is exact:

- own price changes -> move along demand
- non-price determinant changes -> shift demand

Students often say, “Price went up, so demand went down.” That is usually wrong. If the product’s own price rose, the correct statement is: **quantity demanded decreased**.

This matters because AP scoring often rewards precise language. A right graph with wrong vocabulary can still cost points.

> **Test Tip:** On AP questions, first ask: “Did the price of the good itself change?” If yes, it is movement along the curve. If no, look for a demand shifter.

A useful memory aid is **TIRES**:

- **T**astes
- **I**ncome
- **R**elated goods
- **E**xpectations
- **S**ize of market

Some classes use **SPICE** instead. Either is fine as long as your economics is correct.

### The main demand determinants that shift the curve

A demand curve shifts right when consumers want more at every price. It shifts left when consumers want less at every price. The five major shifters are below.

#### Tastes and preferences

If consumers like a product more, demand increases. If they like it less, demand decreases.

Examples:

- a health report says oatmeal is good for heart health -> demand for oatmeal shifts right
- a fashion item goes out of style -> demand shifts left

Why does this shift the whole curve? Because preference changes do not affect just one price. They affect willingness to buy across all prices.

#### Income

Income is one of the easiest shifters to test and one of the easiest to get wrong, because not all goods respond the same way.

> **Key Term: normal good**
> A good for which demand rises when income rises and falls when income falls.
>
> **Key Term: inferior good**
> A good for which demand falls when income rises and rises when income falls.

For **normal goods**, higher income means people can afford more, so demand rises. Examples often include restaurant meals, newer clothing, or vacations.

For **inferior goods**, higher income means people buy less because they switch to alternatives they prefer. Examples may include instant noodles, generic brands, or used clothing in some contexts.

The key is not whether a good is “bad.” Inferior means demand moves opposite to income.

Worked reasoning:

- household income rises
- if the good is a normal good, people buy more at each price
- demand shifts right

But:

- household income rises
- if the good is an inferior good, people now replace it with preferred alternatives
- demand shifts left

Students often assume all goods are normal goods. On AP questions, never assume. Read the wording.

#### Prices of related goods

Related goods come in two main types: substitutes and complements.

> **Key Term: substitute**
> A good that can be used in place of another good.
>
> **Key Term: complement**
> A good that is used together with another good.

For **substitutes**, the relationship is direct.

If the price of coffee rises, some consumers switch to tea. The demand for tea rises. Tea’s demand curve shifts right.

Important detail: the demand curve for coffee does **not** shift from coffee’s own price change. Coffee experiences a movement along its own curve, while tea’s demand curve shifts.

For **complements**, the relationship is inverse.

If the price of printers rises, fewer printers are bought. Since ink cartridges are used with printers, demand for ink cartridges falls. The ink demand curve shifts left.

Worked comparison:

- price of substitute rises -> demand for the other good rises
- price of complement rises -> demand for the other good falls

That direction difference is a classic AP trap.

> **Test Tip:** If two goods compete, think “same direction.” If two goods are used together, think “opposite direction.”

#### Expectations

Expectations affect current demand because buyers act now based on what they think will happen later.

If consumers expect laptop prices to rise next month, many buy now. Current demand rises.

If consumers expect home prices to fall soon, many wait. Current demand falls.

This is a common point students miss: expectations about the future can shift demand **today**.

#### Number of buyers or market size

Market demand is the sum of individual demands. More buyers means more total demand at every price.

If a city gains population, demand for apartments, groceries, and public transportation may increase. If population falls, market demand may decrease.

This is why “population” and “number of buyers” are usually treated as the same demand shifter.

A subtle point: composition matters too. A region with more retirees may have higher demand for healthcare services but not necessarily for school supplies.

### How demand shifts affect equilibrium

Once demand shifts, AP questions often ask what happens to equilibrium price and equilibrium quantity. Assume supply stays constant unless the question says otherwise.

If demand increases, the demand curve shifts right.

That creates upward pressure on price because more buyers want the product at the old price. Sellers respond, and the market moves to a new equilibrium with:

- higher equilibrium price
- higher equilibrium quantity

If demand decreases, the demand curve shifts left.

That creates downward pressure on price because fewer buyers want the product at the old price. The new equilibrium has:

- lower equilibrium price
- lower equilibrium quantity
  > **Key Term: equilibrium**
  > The market outcome where quantity demanded equals quantity supplied.

Here is the cause-and-effect chain for an increase in demand:

1. non-price determinant changes
2. demand shifts right
3. at the old price, quantity demanded exceeds quantity supplied
4. shortage appears
5. price is bid up
6. firms supply more along the existing supply curve
7. new equilibrium has higher price and higher quantity

For a decrease in demand:

1. non-price determinant changes
2. demand shifts left
3. at the old price, quantity supplied exceeds quantity demanded
4. surplus appears
5. price falls
6. firms supply less along the existing supply curve
7. new equilibrium has lower price and lower quantity

Notice what stays constant: the **supply curve**. Sellers move along supply because price changes during adjustment, but supply itself does not shift.

This is another point AP questions target. If demand rises, do not say supply rose unless a supply shifter also changed. Instead say **quantity supplied increased** because of the higher equilibrium price.

Worked example:

Suppose consumer preferences for electric scooters increase.

Step 1: Identify the shifter  
Preferences changed -> demand shifts right.

Step 2: Direction  
Increase in demand -> rightward shift.

Step 3: Equilibrium effect with supply constant  
Equilibrium price rises.  
Equilibrium quantity rises.

Correct AP-style explanation:  
Because consumer preferences improved, demand for electric scooters increased. The demand curve shifts right. With supply unchanged, equilibrium price and equilibrium quantity both increase.

### How to answer AP-style demand-shifter questions

Most errors happen because students jump to the answer before classifying the event.

Use this method every time:

1. Identify the market named in the question
2. Ask whether the product’s own price changed
3. If not, identify the non-price determinant
4. Decide whether demand increases or decreases
5. State right or left shift
6. If asked, state the equilibrium effect

Worked mini-examples:

#### Example 1: “The price of tacos falls.”

This is the product’s own price.  
Result: quantity demanded increases.  
Graph: movement down along the demand curve.  
Not a shift.

#### Example 2: “Consumer income rises, and the good is normal.”

Income is a demand shifter.  
Normal good means income and demand move together.  
Result: demand increases.  
Graph: demand shifts right.

#### Example 3: “The price of gasoline rises, and SUVs are complements with gasoline.”

Related good price changed.  
Gasoline and SUVs are complements.  
Price of complement rises -> demand for SUVs falls.  
Graph: SUV demand shifts left.

#### Example 4: “Consumers expect smartphone prices to be lower next month.”

Expectation changes current behavior.  
If buyers wait, current demand falls.  
Graph: demand shifts left.

A final warning for macro students: this topic is about **product-market demand**, not **aggregate demand**. Here, we are talking about one good such as coffee, cars, or movie tickets. Later in macro, aggregate demand means total demand in the whole economy. The graphs and shifters are different.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Demand shows how much consumers are willing and able to buy at different prices
- A change in the good’s own price causes a change in quantity demanded, not a shift in demand
- A change in quantity demanded is shown as movement along an existing demand curve
- A change in demand is caused by a non-price determinant and shifts the whole curve
- An increase in demand shifts the demand curve right, while a decrease shifts it left
- Main demand shifters include tastes, income, related goods, expectations, and number of buyers
- For a normal good, higher income increases demand
- For an inferior good, higher income decreases demand
- If the price of a substitute rises, demand for the other good rises
- If the price of a complement rises, demand for the other good falls
- With supply constant, an increase in demand raises equilibrium price and quantity
- Product demand in Unit 1 is different from aggregate demand later in AP Macroeconomics

## Key Terms and Concepts

- demand
- quantity demanded
- change in quantity demanded
- change in demand
- normal good
- inferior good
- substitute
- complement
- equilibrium


Demand - Demand determinants shift demand curve