Elasticity - Income Elasticity of Demand

As we know, however, there are large differences between the impact of a change in income on the demand for toothpaste and vacations, even though both are normal goods. This has lead economists to subdivide normal goods into two categories.

Two Types of Normal Goods
Necessities: are goods for which the change in desired quantity demanded is smaller in percentage terms than the change in income, but in the same direction. This means that .
Luxuries: are goods for which the change in desired quantity demanded is greater in percentage terms than the change in income, but in the same direction. This means that .