to a shift of the entire demand curve. The term change in quantity
demanded refers to a movement from one point on a demand curve to
another point, either on the same demand curve or on a new one.
A change in quantity demanded can result from a shift in the demand curve with the price
constant, from a movement along a given demand curve due to a change in the price, or from
a combination of the two. [ 3 ]We consider these three possibilities in turn.
An increase in demand means that the whole demand curve shifts to the
right; at any given price, an increase in demand causes an increase in
quantity demanded. For example, in Figure 3-2 the shift in the demand
curve for apples from to represents an increase in demand, and at a
price of $40 per bushel, quantity demanded increases from 85 000 bushels
to 115 000 bushels, as indicated by the move from V to.
A movement up and to the left along a demand curve represents a
reduction in quantity demand in response to a higher price. For example,
in Figure 3-2 , with the demand for apples given by the curve an
increase in price from $40 to $60 per bushel causes a movement along
from to and quantity demanded decreases from 115 000 bushels to
95 000 bushels.
When there is a change in demand and a change in the price, the overall
change in quantity demanded is the net effect of the shift in the demand
curve and the movement along the new demand curve. Figure 3-4
D 0 D 1V′ D 1 ,V′ W′,