Understanding Demand and Supply

1. The Concept of Demand

In economics, "demand" isn't just about wanting something. It's more specific: it refers to the quantities of a good or service that consumers are both willing and able to buy at various prices over a specific period, holding all other factors constant.

The relationship between the price of a good and the quantity consumers are willing to buy is governed by a fundamental principle: the Law of Demand.

The Law of Demand states that, all else being equal (ceteris paribus), as the price of a good increases, the quantity demanded for that good decreases. Conversely, as the price of a good decreases, the quantity demanded increases. There is an inverse relationship between price and quantity demanded.

To get a clear, intuitive introduction to these ideas, let's watch a short video.

This inverse relationship is what gives the demand curve its characteristic downward slope. By convention, economists place Price on the vertical (y) axis and Quantity on the horizontal (x) axis.

The Demand Function

For the CFA exam, you'll need to be comfortable with a more formal, mathematical representation of demand. The relationship between quantity demanded and its various determinants is expressed through a demand function.

While many factors influence demand (like income, tastes, and prices of other goods), the Law of Demand focuses on the effect of the good's own price. To do this, we hold the other factors constant.

The following video explains how a general demand function is used to derive a specific demand curve. It also introduces the concept of the inverse demand function, which is what we actually plot on the graph (with Price as a function of Quantity).

2. The Concept of Supply

Now let's turn to the other side of the market: the sellers.

Supply refers to the quantities of a good or service that producers are both willing and able to offer for sale at various prices over a period, holding other factors constant.

Just as with demand, there is a fundamental law governing this relationship: the Law of Supply.

The Law of Supply states that, all else being equal (ceteris paribus), as the price of a good increases, the quantity supplied of that good also increases. Conversely, as the price decreases, the quantity supplied decreases. There is a direct relationship between price and quantity supplied.

The underlying "why" for this law is the profit motive. Higher prices, assuming costs remain the same, mean higher potential profits, which creates an incentive for producers to supply more.

Let's return to the video from Professor Dave for a simple explanation of supply.

This direct relationship gives the supply curve its upward slope, as seen in the blue line in the graph we looked at earlier. A higher price corresponds to a higher quantity supplied.

Similar to demand, supply can be represented by a supply function. For example, a simple supply function might be $Q_S=-10+2P$, where $Q_S$ is quantity supplied and $P$ is price. The positive coefficient on price (2) reflects the direct relationship of the Law of Supply.

To reinforce the formal definitions used in CFA materials, take a moment to read these precise statements of both laws.

3. Application and Practice

Your preference for combining theory with practice is key to mastering economics. Let's apply what we've just learned by tackling some CFA-style questions. This will help solidify your understanding and highlight the level of precision required for the exam.

How did you find those questions? Notice the precision in the wording. For example, question 11 emphasizes the "inverse relation between price and the quantity demanded," not between price and "demand." This is a critical distinction that we will explore fully in our next lesson. A change in a good's own price causes a change in quantity demanded (a movement along the curve), while a change in another factor causes a change in demand itself (a shift of the entire curve).

Conclusion

In this introductory lesson, we have laid the essential groundwork for market analysis. You should now be comfortable with the core definitions and laws that govern the behavior of buyers and sellers.

Key Takeaways:

• Demand: The relationship between the price of a good and the quantity consumers are willing and able to purchase.
• Law of Demand: A fundamental principle stating that price and quantity demanded are inversely related, leading to a downward-sloping demand curve.
• Supply: The relationship between the price of a good and the quantity producers are willing and able to sell.
• Law of Supply: A fundamental principle stating that price and quantity supplied are directly related, leading to an upward-sloping supply curve.
• The phrase ceteris paribus (all else being equal) is a crucial assumption for both laws, as it isolates the effect of a good's own price.

Preview of the Next Lesson:

We've established the basic laws by assuming "all else is equal." In our next session, we will relax this assumption. We'll explore the factors other than price that influence buying and selling decisions and learn to distinguish between a movement along a demand or supply curve and a shift of the entire curve. This distinction is fundamental to analyzing how markets respond to changing economic conditions.