Back to the Curve
A change in overall demand represents a shift in demand, upward or downward. That means that one or more of the factors I just discussed can cause the entire demand curve to shift to the right (upward) or to the left (downward), as shown in Figure 4.2 (on the next page).
A shift in demand is different from a change in the quantity demanded because of a change in the price. If the supermarket chain lowers the price of beef from $8 to $6 and sees its sales increase from 40,000 to 60,000 pounds, the price change caused a change in the quantity demanded. That change represents movement along the demand curve—that is, along the curve D, the middle curve of the three curves in Figure 4.2.
A shift in demand occurs when the whole ...