The article discusses how the price of a product affects how much people buy it. It also talks about how prices of different products and people's incomes can change how much they buy. The researchers give examples and talk about how companies can use this information to set prices. They also mention recent studies on what influences pricing decisions. The article explains how the prices of different products can affect each other and how this can help understand different markets. Lastly, it connects people's incomes to how much they buy.