AP MicroeconomicsConsumer Choice
Engel Curve
An Engel curve shows how the quantity of a good a consumer buys changes as income changes, holding prices constant: upward-sloping for normal goods, downward for inferior goods.
Named after statistician Ernst Engel, the curve plots income against quantity demanded of a single good. A normal good has an upward-sloping Engel curve (more income, more bought), while an inferior good has a downward-sloping one over some income range. The steepness reflects income elasticity: necessities flatten as income rises (income elasticity between 0 and 1), whereas luxuries rise more than proportionally (income elasticity above 1). It is the income analogue of the ordinary (price) demand curve.