Recent research confirms that the demand for cigarettes is not only price inelastic, but it also indicates smokers with incomes in the lower half of all incomes respond to a given price increase by reducing their purchases by amounts that are more than four times as large as the purchase reductions made by smokers in the upper half of all incomes.

How can the income and substitution effects of a price change help explain this?

Review price elasticity of demand and supply. Price elasticity describes the sensitivity between quantity demanded/supplied and price when a change in price occurs. A relatively lower change in quantity versus a change in price means the product is more price inelastic; a higher relative change in quantity versus a price change indicates more price elastic. Review the substitution effect and income effect dynamics.