A decrease in supply can be noted by observing what in a market graph?

In a market graph, a decrease in supply is indicated by a leftward shift in the supply curve. This shift reflects a reduction in the quantity of goods or services that producers are willing and able to sell at each price level. When the supply curve shifts to the left, it signifies that fewer products are available in the market, which often leads to higher equilibrium prices if demand remains constant. This is a fundamental concept in microeconomics, as it illustrates the relationship between supply levels and market equilibrium.

In contrast, an increase in demand would lead to a higher quantity being demanded at every price, which does not represent a decrease in supply. A rightward shift in the supply curve indicates an increase in supply, which is the opposite of what is being asked. A plateau in prices might occur due to various factors but does not specifically indicate a decrease in supply on its own. Therefore, the correct identification of a leftward shift truly encapsulates the concept of declining supply levels in a market scenario.