Which factor does NOT affect demand?

Demand for a good or service is influenced by several factors, including market size, consumer income, and preferences. Each of these elements can lead to shifts in the demand curve.

Market size affects demand because an increase in the number of consumers typically raises the overall demand for a product. Changes in consumer income can shift demand as well; for instance, an increase in income generally leads to an increase in demand for normal goods, while a decrease could lower demand. Additionally, changes in consumer preferences or tastes can significantly influence demand, as shifts towards favoring a particular product can lead those consumers to purchase more of it.

Supply, however, relates more directly to the ability and willingness of producers to sell a good or service at a given price. While changes in supply can impact market equilibrium and the price of goods, they do not directly alter demand. Therefore, supply does not play a role in shifting the demand curve and is the correct answer as the factor that does not affect demand.