One of the things economists do is to study the relationship between the supply of products being sold on the market, the demand for products by consumers, and the price of products. They look at how price is determined by the availability of a product (the supply), and by the number of people hoping to buy the product (the demand). Changes in either the supply or the demand will almost certainly affect the price, which in turn will affect how many people are willing to sell the product (supply) or buy the product (demand).