A change in supply is a shift in the entire supply curve either to the left (a decrease in supply) or to the right (an increase in supply).A change in supply, therefore, is a change in the entire supply schedule or curve.In contrast, a change in quantity supplied is a movement along an existing supply curve or schedule from one price-quantity combination to another.A change in product price causes the change in quantity supplied.
(a) Consumers' tastes become less favourable toward the item.
(b) The number of buyers decreases.
(c) Incomes fall and the item is a normal good or incomes rise and the item is an inferior good.
(d) A decrease in the price of a substitute product or an increase in the price of a complementary product.
(e) Consumers expect lower prices in the future.
Substitute goods are those that can be used in place of each other.The price of the substitute and demand for the other good are directly related.If the price of Coke rises, demand for Pepsi should increase.Complementary goods are those that are used together like tennis balls and rackets.When goods are complements, there is an inverse relationship between the price of one and the demand for the other.Some goods are not related to each other and are independent goods.In these cases, a change in price of one will not affect the demand for the other.