Elasticity of Demand

Elasticity of Demand
 Price elasticity measures the responsiveness of the quantity demanded or supplied of a good
to a change in its price. It is computed as the percentage change in quantity demanded—or
supplied—divided by the percentage change in price.
 Elasticity can be described as elastic—or very responsive—unit elastic, or inelastic—not very

responsive.
 Elastic demand or supply curves indicate that the quantity demanded or supplied responds to
price changes in a greater than proportional manner.
 An inelastic demand or supply curve is one where a given percentage change in price will cause
a smaller percentage change in quantity demanded or supplied.
 Unitary elasticity means that a given percentage change in price leads to an equal percentage
change in quantity demanded or supplied.
What is price elasticity?
Both demand and supply curves show the relationship between price and the number of units
demanded or supplied. Price elasticity is the ratio between the percentage change in the
quantity demanded, or supplied and the corresponding percent change in price.
The price elasticity of demand is the percentage change in the quantity demanded of a good
or service divided by the percentage change in the price. The price elasticity of supply is the
percentage change in quantity supplied divided by the percentage change in price.
Elasticities can be usefully divided into five broad categories: perfectly elastic, elastic,
perfectly inelastic, inelastic, and unitary. An elastic demand or elastic supply is one in which
the elasticity is greater than one, indicating a high responsiveness to changes in price.
An inelastic demand or inelastic supply is one in which elasticity is less than one, indicating
low responsiveness to price changes. Unitary elasticities indicate proportional responsiveness
of either demand or supply.
Perfectly elastic and perfectly inelastic refer to the two extremes of elasticity. Perfectly elastic
means the response to price is complete and infinite: a change in price results in the quantity
falling to zero. Perfectly inelastic means that there is no change in quantity at all when price
changes.
the midpoint method to calculate elasticity
To calculate elasticity, instead of using simple percentage changes in quantity and price,
economists sometimes use the average percent change in both quantity and price. This is called
the Midpoint Method for Elasticity:
The advantage of the midpoint method is that we get the same elasticity between two price
points whether there is a price increase or decrease. This is because the formula uses the same
base for both cases. The midpoint method is referred to as the arc elasticity in some textbooks.
Using the point elasticity of demand to calculate elasticity
A drawback of the midpoint method is that as the two points get farther apart, the elasticity
value loses its meaning. For this reason, some economists prefer to use the point
elasticity method. In this method, you need to know what values represent the initial values
and what values represent the new values.
Arc Elasticity
Arc elasticity is the elasticity of one variable with respect to another between two given
points. It is used when there is no general function to define the relationship between the two
variables.
Arc elasticity is also defined as the elasticity between two points on a curve. The concept is
used in both mathematics and economics.
The Formula for the Arc Price Elasticity of Demand Is
How to Calculate the Arc Price Elasticity of Demand
If the price of a product decreases from $10 to $8, leading to an increase in quantity
demanded from 40 to 60 units, then the price elasticity of demand can be calculated as:
 % change in quantity demanded = (Qd2 – Qd1) / Qd1 = (60 – 40) / 40 = 0.5

 % change in price = (P2 – P1) / P1 = (8 – 10) / 10 = -0.2
 Thus, PEd = 0.5 / -0.2 = 2.5
What Does Arc Elasticity Tell You?
In economics, there are two possible ways of calculating elasticity of demand—price (or
point) elasticity of demand and arc elasticity of demand. The arc price elasticity of
demand measures the responsiveness of quantity demanded to a price. It takes the elasticity
of demand at a particular point on the demand curve, or between two points on the curve.
 In the concept of arc elasticity, elasticity is measured over the arc of the demand curve
on a graph.
 Arc elasticity calculations give the elasticity using the midpoint between two points.
 The arc elasticity is more useful for larger price changes and gives the same elasticity
outcome whether price falls or rises.
Arc Elasticity of Demand

One of the problems with the price elasticity of demand formula is that it gives different
values depending on whether price rises or falls. If you were to use different start and end
points in our example above—that is, if you assume the price increased from $8 to $10—and
the quantity demanded decreased from 60 to 40, the Ped will be:
 % change in quantity demanded = (40 – 60) / 60 = -0.33

 % change in price = (10 – 8) / 8 = 0.25
 PEd = -0.33 / 0.25 = 1.32, which is much different from 2.5
To eliminate this problem, the arc elasticity can be used. Arc elasticity measures elasticity at
the midpoint between two selected points on the demand curve by using a midpoint between
the two points. The arc elasticity of demand can be calculated as:
 Arc Ed = [(Qd2 – Qd1) / midpoint Qd] ÷ [(P2 – P1) / midpoint P]
Cross Elasticity of Demand
The cross elasticity of demand is an economic concept that measures the responsiveness in
the quantity demanded of one good when the price for another good changes. Also called
cross-price elasticity of demand, this measurement is calculated by taking the percentage
change in the quantity demanded of one good and dividing it by the percentage change in the
price of the other good.
 The cross elasticity of demand is an economic concept that measures the

responsiveness in the quantity demanded of one good when the price for another good
changes.
 The cross elasticity of demand for substitute goods is always positive because the
demand for one good increases when the price for the substitute good increases.
 Alternatively, the cross elasticity of demand for complementary goods is negative.
In economics, the elasticity of demand refers to how sensitive the demand for a good is to
changes in other economic variables, such as price or consumer income.
Substitute Goods
The cross elasticity of demand for substitute goods is always positive because the demand for
one good increases when the price for the substitute good increases. For example, if the price
of coffee increases, the quantity demanded for tea (a substitute beverage) increases as
consumers switch to a less expensive yet substitutable alternative. This is reflected in the
cross elasticity of demand formula, as both the numerator (percentage change in the demand
of tea) and denominator (the price of coffee) show positive increases.
Items with a coefficient of 0 are unrelated items and are goods independent of each
other. Items may be weak substitutes, in which the two products have a positive but low cross
elasticity of demand. This is often the case for different product substitutes, such as tea versus
coffee. Items that are strong substitutes have a higher cross-elasticity of demand. Consider
different brands of tea; a price increase in one company’s green tea has a higher impact on
another company’s green tea demand.
Complementary Goods
Alternatively, the cross elasticity of demand for complementary goods is negative. As the
price for one item increases, an item closely associated with that item and necessary for its
consumption decreases because the demand for the main good has also dropped.
For example, if the price of coffee increases, the quantity demanded for coffee stir sticks
drops as consumers are drinking less coffee and need to purchase fewer sticks. In the
formula, the numerator (quantity demanded of stir sticks) is negative and the denominator
(the price of coffee) is positive. This results in a negative cross elasticity.
Toothpaste is an example of a substitute good; if the price of one brand of toothpaste

increases, the demand for a competitor's brand of toothpaste increases in turn.
Usefulness of Cross Elasticity of Demand

Companies utilize cross-elasticity of demand to establish prices to sell their goods. Products
with no substitutes have the ability to be sold at higher prices because there is no cross-
elasticity of demand to consider. However, incremental price changes to goods with
substitutes are analyzed to determine the appropriate level of demand desired and the
associated price of the good.
Additionally, complementary goods are strategically priced based on cross-elasticity of

demand. For example, printers may be sold at a loss with the understanding that the demand
for future complementary goods, such as printer ink, should increase.

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Elasticity of Demand

 Elasticity can be described as elastic—or very responsive—unit elastic, or inelastic—not very

What is price elasticity?

the midpoint method to calculate elasticity

Using the point elasticity of demand to calculate elasticity

The Formula for the Arc Price Elasticity of Demand Is

How to Calculate the Arc Price Elasticity of Demand

 % change in quantity demanded = (Qd2 – Qd1) / Qd1 = (60 – 40) / 40 = 0.5

Arc Elasticity of Demand

 % change in quantity demanded = (40 – 60) / 60 = -0.33

 Arc Ed = [(Qd2 – Qd1) / midpoint Qd] ÷ [(P2 – P1) / midpoint P]

Cross Elasticity of Demand

 The cross elasticity of demand is an economic concept that measures the

Toothpaste is an example of a substitute good; if the price of one brand of toothpaste

Usefulness of Cross Elasticity of Demand

Additionally, complementary goods are strategically priced based on cross-elasticity of

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