Income elasticity of demand measures how responsive the demand for a particular good or service is to changes in consumer income. It tells us how much the demand for a product will change if there is a change in consumer income.If the income elasticity of demand is positive, it means that as consumer income increases, the demand for the product also increases. That's because people tend to buy more of a product when they have more money. So, in this case, the product is considered to be a normal good.On the other hand, if the income elasticity of demand is negative, it means that as consumer income increases, the demand for the product decreases. This is because people tend to switch to better quality products when their income increases and the product is considered inferior.