The Factors that affect the demand are First, Willingness to buy convey a desire, based on what economists call tastes and preferences. You may need nor want something, you will not buy it then the Ability to buy convey that income is important. Second, size or composition of the population can affect demand. The more children a family has, the greater their demand for clothing. There is a need for the Consumer to understand the changes because if there is greater demand there is a greater supply.