The factors that will determine the level of demand at a given price e.g. population.
Below is a list of factors that will cause the demand of a given product to change. If the price of substitute goods change this will change the demand for a product as consumers will always switch to the cheapest versions of a product. If the price of complementary goods change this will affect the demand for a product as consumers will always consume both complimentary goods together. Changes in real income will affect the demand of a good because the more income that consumers have available to them the mre goods they are likely to demand and consume. The persuasion of advetising and marketing campaigns can sway consumers towards purchasing goods. Finally a change in fashion, tastes and preferences can also affect demand for products, this often happens in the clothing industry when certain clothing items come back into fashion .