Price elasticity of demand is to sensitivity of quantity demanded as income elasticity is to what?

Price elasticity of demand measures how much the quantity demanded of a good changes when its price changes. In a similar way, income elasticity of demand looks at how the quantity demanded changes when consumer income changes. Essentially, while price elasticity focuses on price changes, income elasticity focuses on changes in income levels. For example, if a person's income increases, they might buy more luxury items, showing a positive income elasticity. So, just as price elasticity relates to sensitivity to price changes, income elasticity relates to sensitivity to changes in income.