Video: Change in Demand vs. Change in Quantity Demanded

It’s hard to overstate the importance of understanding the difference between shifts in curves and movements along curves. Remember, when we talk about changes in demand or supply, we do not mean the same thing as changes in quantity demanded or quantity supplied.

A change in demand refers to a shift in the entire demand curve, which is caused by a variety of factors (preferences, income, prices of substitutes and complements, expectations, population, etc.). In this case, the entire demand curve moves left or right.

A supply and demand graph showing three demand curves D0, D1, and D2, with arrows indicating that D0 can shift to become D1 or to D2.

Figure 1. Change in Demand. A change in demand means that the entire demand curve shifts either left or right. The initial demand curve D0 shifts to become either D1 or D2. This could be caused by a shift in tastes, changes in population, changes in income, prices of substitute or complement goods, or changes future expectations.

A change in quantity demanded refers to a movement along the demand curve, which is caused only by a chance in price. In this case, the demand curve doesn’t move; rather, we move along the existing demand curve.

A supply and demand graph showing a single demand curve, D0, with two arrows indicating movement along the curve in either direction.

Figure 2. Change in Quantity Demanded. A change in the quantity demanded refers to movement along the existing demand curve, D0. This is a change in price, which is caused by a shift in the supply curve.