Final answer:
To estimate the price elasticity of demand, economists need to know the price of the product, the quantity demanded of the product, and the availability of substitute products.
Step-by-step explanation:
To estimate the price elasticity of demand, economists need to know the price of the product and the quantity demanded of the product. They also need information about the availability of substitute products.
While the income of consumers can influence demand, it is not directly needed to estimate the price elasticity of demand.