2.4.5. Shifts in the Demand Curve

The demand curve was drawn under the assumption that the consumer’s income, the prices of other goods and the preferences of the consumer are given. What happens to the demand curve when any of these things changes?

The demand curve is a graphical representation of the relationship between the price of a good and the quantity demanded by consumers, holding all other factors constant. When changes occur in factors such as consumer income, prices of related goods, or consumer preferences, the entire demand curve can shift either to the right (indicating an increase in demand) or to the left (indicating a decrease in demand).

For instance, think about how a popular new phone model can shift the demand curve for phone accessories. If a new phone is released and many people want it (possibly due to social media reviews), the demand for cases and chargers shifts to the right, meaning consumers are now buying more cases and chargers at the same price because more people own that new phone.

Given the prices of other goods and the preferences of a consumer, if the income increases, the demand for the good at each price changes, and hence, there is a shift in the demand curve. For normal goods, the demand curve shifts rightward and for inferior goods, the demand curve shifts leftward.

When a consumer's income increases, they generally have more money to spend. For normal goods, which are those goods that consumers buy more of as their income increases, this results in an outward shift of the demand curve to the right. In contrast, for inferior goods, which are goods that consumers buy less of as their income increases (such as instant noodles or second-hand clothing), the demand curve shifts to the left.

Imagine a family that traditionally buys budget-brand pasta due to their lower income. If they receive a raise, they might start buying a premium brand instead. Hence, the demand for the budget pasta decreases, shifting its demand curve leftward, while the demand for the premium pasta shifts rightward.

Given the consumer’s income and her preferences, if the price of a related good changes, the demand for a good at each level of its price changes, and hence, there is a shift in the demand curve. If there is an increase in the price of a substitute good, the demand curve shifts rightward. On the other hand, if there is an increase in the price of a complementary good, the demand curve shifts leftward.

When the price of a substitute good (like tea) increases, consumers will likely shift their demand to a substitutable item (like coffee), resulting in a rightward shift of the demand curve for coffee. In contrast, if the price of a complement (like printers) rises, fewer customers will buy printers and therefore less ink will be demanded, causing a leftward shift for ink.

For instance, if the price of coffee rises significantly, many coffee drinkers may switch to tea, increasing the demand for tea. Conversely, if the price of printers rises, people might buy fewer printers and hence less printer ink, thereby decreasing the demand for ink.

The demand curve can also shift due to a change in the tastes and preferences of the consumer. If the consumer’s preferences change in favour of a good, the demand curve for such a good shifts rightward. On the other hand, the demand curve shifts leftward due to an unfavourable change in the preferences of the consumer.

Changes in consumer preferences can significantly influence demand. If something becomes fashionable or trendy, like plant-based foods, the demand curve will shift to the right, indicating an increase in quantity demanded at all price levels. Conversely, if new health information emerges that paints a product in a negative light, the demand can decrease and shift leftward.

For example, suppose a new study comes out linking sugary drinks to health problems. If consumers start to prefer healthier options or switch to water, the demand curve for sugary drinks will shift to the left, while the demand curve for bottled water or healthy drinks will shift to the right.

Shifts in demand curve are depicted in Figure 2.16. It may be mentioned that shift in the demand curve takes place when there is a change in some factor, other than the price of the commodity.

In graphical representations, the movement of the entire demand curve to the left or right illustrates how demand changes without altering the price. This simple yet powerful visualization allows economists to convey the effects of changing conditions on consumer behavior effectively.

Consider the video game market. If a popular gaming console is released and positively received, everyone wants it. As demand rises, the demand curve shifts right. However, if a competing console with better features comes in, it may cause a leftward shift for the first console, depicting a decrease in its demand.

--