Types
of Elasticity of Demand:
The quantity of a commodity demanded per unit of time
depends upon various factors such as the price of a commodity, the money income
of the prices of related goods, the tastes of the people, etc., etc.
Whenever there is a change in any of the variables
stated above, it brings about a change in the quantity of the commodity
purchased over a specified period of time. The elasticity of demand measures the
responsiveness of quantity demanded to a change in any one of the above factors
by keeping other factors constant. When the relative responsiveness or
sensitiveness of the quantity demanded is measured to changes, in its price, the
elasticity is said be price elasticity of demand.
When the change in demand is the result of the given
change in income, it is named as income elasticity of demand. Sometimes, a
change in the price of one good causes a change in the demand for the other. The
elasticity here is called cross electricity of demand. The three main
types of elasticity of demand are now discussed in brief.
(1)
Price Elasticity of Demand:
Definition and Explanation:
The concept of price elasticity of demand is commonly
used in economic literature. Price elasticity of demand is the degree of
responsiveness of quantity demanded of a good to a change in its price.
Precisely, it is defined as:
"The
ratio of proportionate change in the quantity demanded of a good caused by a
given proportionate change in price".
Formula:
The formula for measuring price elasticity of demand
is:
Price Elasticity of Demand = Percentage in
Quantity Demand
Percentage
Change in Price
E_{d} = Δq
X P
Δp Q
Example:
Let us suppose that
price of a good falls from $10 per unit to
$9 per unit in a day. The
decline in price causes the quantity of the good demanded to increase from 125
units to 150 units per day. The price elasticity using the simplified formula
will be:
E_{d} = Δq X
P
Δp Q
Δq = 150 
125 = 25
Δp = 10  9 = 1
Original
Quantity = 125
Original
Price = 10
E_{d} = 25 / 1 x 10 / 125 =
2
The
elasticity coefficient is greater than one. Therefore the
demand for the good is elastic.
Types:
The
concept of price elasticity of demand can be used to divide the goods in to
three groups.
(i) Elastic. When the percent change in
quantity of a good is greater than the percent change in its price, the demand
is said to be elastic. When elasticity of demand is greater than one, a fall in
price increases the total revenue (expenditure) and a rise in price lowers the
total revenue (expenditure).
(ii) Unitary Elasticity. When the percentage
change in the quantity of a good demanded equals percentage in its price, the
price elasticity of demand is said to have unitary elasticity. When elasticity
of demand is equal to one or unitary, a rise or fall in price leaves total
revenue unchanged.
(iii) Inelastic. When the percent change in
quantity of a good demanded is less than the percentage change in its price, the
demand is called inelastic. When elasticity of demand is inelastic or less than
one, a fall in price decreases total revenue and a rise in its price increases
total revenue.
(2)
Income Elasticity of Demand:
Definition and Explanation:
Income is an important variable affecting the demand
for a good. When there is a change in the level of income of a
consumer, there is a change in the quantity demanded of a good, other factors
remaining the same. The degree of change or responsiveness of quantity
demanded of a good to a change in the income of a consumer is called income
elasticity of demand. Income elasticity of demand can be defined as:
"The
ratio of percentage change in the quantity of a good purchased, per unit of time
to a
percentage change in the income of a
consumer".
Formula:
The
formula for
measuring the income elasticity of demand is the
percentage change in demand for a good divided by the percentage change in
income. Putting this in symbol gives.
E_{y} = Percentage Change in
Demand
Percentage
Change in Income
Simplified formula:
E_{y }= Δq X
P
Δp Q
Example:
A simple example will show how income elasticity of
demand can be calculated. Let us assume that the income of a person
is $4000 per month and he purchases six CD's per month. Let us assume
that the monthly income of the consumer increase to $6000 and the
quantity demanded of CD's per month rises to eight. The elasticity of
demand for CD's will be calculated as under:
Δq =
8  6 = 2
Δp = $6000  $4000 = $2000
Original
quantity demanded = 6
Original income = $4000
E_{y}
= Δq / Δp x P / Q = 2 / 200 x 4000 / 6 = 0.66
The income elasticity is 0.66 which is less than one.
Types:
When the income of a
person increases, his demand for goods also changes
depending upon whether the good is a normal good or an inferior good. For normal
goods, the value of elasticity is greater than zero but less than one.
Goods with an income elasticity of less than 1 are called inferior goods.
For example, people buy more food as their income rises but the % increase in
its demand is less than the % increase in income.
(3) Cross Elasticity of Demand:
Definition and Explanation:
The concept of cross elasticity of demand is used for
measuring the responsiveness of quantity demanded of a good to
changes in the price of related goods. Cross elasticity of demand is defined
as:
"The
percentage change in the demand of one good as a result of the percentage change
in the price of another good".
Formula:
The formula for measuring, cross, elasticity of
demand is:
E_{xy} =
% Change in Quantity Demanded of Good X
% Change in Price of Good Y
The numerical value of cross elasticity depends on
whether the two goods in question are substitutes, complements or
unrelated.
Types and Example:
(i) Substitute Goods. When two goods are substitute
of each other, such as coke and Pepsi, an increase in the price of one good
will lead to an increase in demand for the other good. The numerical
value of goods is positive.
For example there are two goods. Coke and
Pepsi which are close substitutes. If there is increase in the price
of Pepsi called good y by 10% and it increases the demand for Coke called
good X by 5%, the cross elasticity of demand would be:
E_{xy
}
= %Δq_{x} / %Δp_{y}
= 0.2
Since E_{xy} is positive (E > 0), therefore, Coke and Pepsi are close
substitutes.
(ii) Complementary Goods. However, in case of
complementary goods such as car and petrol, cricket bat and ball, a rise in
the price of one good say cricket bat by 7% will bring a fall in the demand
for the balls (say by 6%). The cross elasticity of demand which are
complementary to each other is, therefore, 6% / 7% = 0.85
(negative).
(iii) Unrelated Goods. The two goods which a
re unrelated to each other, say apples and pens, if the price of apple rises in
the market, it is unlikely to result in a change in quantity demanded of pens.
The elasticity is zero of unrelated goods.
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