Download Shifts in the Demand Curve

Movements Along the Demand Curve
Shifts in the Demand Curve
A movement along the demand curve occurs when there is a change in price. The
factors affecting demand are assumed to be held constant. A change in price leads to a
movement along the demand curve and is referred to as a change in quantity
demanded
A shift in the demand curve is caused by a factor affecting demand other than a
change in price. If any of these factors change, then the amount consumers wish to
purchase changes whatever the price. The shift in the demand curve is referred to as an
increase or decrease in demand.
Shifts in the Demand Curve
The demand curve for ice cream, for example, shows how much ice cream people are
willing to buy at any given price, holding constant the many other factors beyond price
that influence consumers’ buying decisions. As a result, this demand curve need not be
stable over time. If something happens to alter the quantity demanded at any given
price, the demand curve shifts.
For example, suppose European health authorities discovered that people who
regularly eat ice cream live longer, healthier lives. The discovery would raise the
demand for ice cream. At any given price, buyers would now want to purchase a
larger quantity of ice cream and the demand curve for ice cream would shift.
Any change that increases the quantity demanded at every price, such as our imaginary
discovery by the European health authorities, shifts the demand curve to the right and is
called an increase in demand. Any change that reduces the quantity demanded at every
price shifts the demand curve to the left and is called a decrease in demand.
Variables that Cause the Demand to Shift
There are many variables that can shift the demand curve. Here are the most important.
Income
What would happen to the demand for ice cream if unemployment increases?
Most likely, it would fall because of lower incomes. Lower incomes mean that
people have less to spend in total, so they are likely to spend less on some – and
probably most – goods. If the demand for a good falls when income falls, the
good is called a normal good.
Not all goods are normal goods. If the demand for a good rises when income
falls, the good is called an inferior good. An example of an inferior good might be
bus rides. As income falls, people are less likely to buy a car or take a taxi and
more likely to take the bus. As income falls, therefore, demand for bus rides
tends to increase.
Prices of Related Goods
SUBSTITUTES:
Suppose that the price of water ice falls. The law of demand says that
people will buy more water ice. At the same time, people will probably buy
less ice cream. Because ice cream and water ice are both frozen and
sweet, they satisfy similar desires. When a fall in the price of one good
reduces the demand for another good, the two goods are called
substitutes. Substitutes are often pairs of goods that are used in place of
each other, such as beef steak and Wiener schnitzel, pullovers and
sweatshirts, and cinema tickets and DVD rentals. The more closely related
substitute products are the more effect we might see on demand if the
price of one of the substitutes changes.
COMPLEMENTS
Now suppose that the price of chocolate sprinkles falls. According to the
law of demand, people will buy more chocolate sprinkles. Yet, in this case,
people will buy more ice cream as well, because ice cream and chocolate
bars are often used together. When a fall in the price of one good raises
the demand for another good, the two goods are called complements.
Complements are often pairs of goods that are used together, such as
gasoline and cars, computers and software, bread and cheese,
strawberries and cream, and bacon and eggs.
Tastes
The most obvious determinants of demand are tastes and fashions. If people like
ice cream, they buy more of it. Economists are increasingly interested in
explaining people’s tastes. The developments in neuroscience mean that we now
have an increasing understanding of why people make decisions and this has
come into the realm of economics. This helps economists examine why and what
happens when tastes change.
Expectations
People’s expectations about the future may affect their demand for a good or
service today. For example, if people expect to earn a higher income next month,
they may be more willing to spend some of their current savings buying ice
cream. As another example, if people expect the price of ice cream to fall
tomorrow, they may be less willing to buy an ice cream cornet at today’s price.
The Size and Structure of the Population
A larger population, other things being equal, will mean a higher demand for all
goods and services. Changes in the way the population is structured also
influences demand. Many European countries have an ageing population and
this leads to a change in the demand. Goods and services required by the elderly
increase in demand as a result. The demand for retirement homes, insurance
policies suitable for elderly drivers and smaller cars may increase as a result.
Summary
The demand curve shows what happens to the quantity demanded of a good when its
price varies, holding constant all the other variables that influence buyers. When one or
more of these other variables changes, the demand curve shifts leading to an increase
or decrease in demand.
Variables that Influence Buyers
Variable
A change in this variable...
Price
Represents a movement along the demand curve
Income
Shifts the demand curve
Price of related
goods
Shifts the demand curve
Tastes
Shifts the demand curve
Expectations
Shifts the demand curve
Number of buyers
Shifts the demand curve
Case Study
Public policy makers often want to reduce the amount that people smoke. There are two
ways that policy can attempt to achieve this goal.
One way to reduce smoking is to shift the demand curve for cigarettes and other
tobacco products. Anti-smoking campaigns on television, mandatory health
warnings on cigarette packages and the prohibition of cigarette advertising are all
policies aimed at reducing the quantity of cigarettes demanded at any given
price. If successful, these policies shift the demand curve for cigarettes to the left.
There is another way policy makers can try to raise the price of cigarettes. If the
government taxes the manufacture of cigarettes, for example, cigarette
companies pass much of this tax on to consumers in the form of higher prices. A
higher price encourages smokers to reduce the numbers of cigarettes they
smoke. In this case, the reduced amount of smoking does not represent a shift in
the demand curve. Instead, it represents a movement along the same demand
curve to a point with a higher price and lower quantity.
How much does the amount of smoking respond to changes in the price of cigarettes?
Economists have attempted to answer this question by studying what happens when
the tax on cigarettes changes. They have found that a 10 per cent increase in the price
causes about a 4 per cent reduction in the quantity demanded. Teenagers are found to
be especially sensitive to the price of cigarettes; a 10 per cent increase in the price
causes about a 12 per cent drop in teenage smoking
Testing questions
1. Explain the outcome of each of the following statements and show what it might look
like on the graphs to the right:
The market for large family cars
if people decide to have more children.
The market for large family cars if the price of
gasoline and diesel increases.
The government raises increases the tax on
large cars.
The demand for small cars as a result of an
increase in tax on large cars.
The market for large family cars if the
people’s incomes rise.
Explain what is meant by an inferior good and provide an example.