Why The Aggregatesupply Curve Slopes Upward In The Short

We now come to the key difference between the economy in the short run and in the long run: the behavior of aggregate supply. As we have already discussed, the long-run aggregate-supply curve is vertical. By contrast, in the short run, the aggregate-supply curve is upward sloping, as shown in Figure 31-6. That is, over a period of a year or two, an increase in the overall level of prices in the economy tends to raise the quantity of goods and services supplied, and a decrease in the level of prices tends to reduce the quantity of goods and services supplied.

What causes this positive relationship between the price level and output? Macroeconomists have proposed three theories for the upward slope of the short-run aggregate-supply curve. In each theory, a specific market imperfection causes the supply side of the economy to behave differently in the short run than it does in the long run. Although each of the following theories will differ in detail, they share a common theme: The quantity of output supplied deviates from its longrun, or "natural," level when the price level deviates from the price level that people expected. When the price level rises above the expected level, output rises above its natural rate, and when the price level falls below the expected level, output falls below its natural rate.

Figure 31-6

The Short-Run Aggregate-Supply Curve. In the short run, a fall in the price level from P1 to P2 reduces the quantity of output supplied from Y1 to Y2. This positive relationship could be due to misperceptions, sticky wages, or sticky prices. Over time, perceptions, wages, and prices adjust, so this positive relationship is only temporary.

Price Level

Price Level

Short-run aggregate supply

2. . . . reduces the quantity of goods and services

2. . . . reduces the quantity of goods and services

Output

Output

The Misperceptions Theory One approach to the short-run aggregate-supply curve is the misperceptions theory. According to this theory, changes in the overall price level can temporarily mislead suppliers about what is happening in the individual markets in which they sell their output. As a result of these short-run misperceptions, suppliers respond to changes in the level of prices, and this response leads to an upward-sloping aggregate-supply curve.

To see how this might work, suppose the overall price level falls below the level that people expected. When suppliers see the prices of their products fall, they may mistakenly believe that their relative prices have fallen. For example, wheat farmers may notice a fall in the price of wheat before they notice a fall in the prices of the many items they buy as consumers. They may infer from this observation that the reward to producing wheat is temporarily low, and they may respond by reducing the quantity of wheat they supply. Similarly, workers may notice a fall in their nominal wages before they notice a fall in the prices of the goods they buy. They may infer that the reward to working is temporarily low and respond by reducing the quantity of labor they supply. In both cases, a lower price level causes misperceptions about relative prices, and these misperceptions induce suppliers to respond to the lower price level by decreasing the quantity of goods and services supplied.

The Sticky-Wage Theory A second explanation of the upward slope of the short-run aggregate-supply curve is the sticky-wage theory. According to this theory, the short-run aggregate-supply curve slopes upward because nominal wages are slow to adjust, or are "sticky," in the short run. To some extent, the slow adjustment of nominal wages is attributable to long-term contracts between workers and firms that fix nominal wages, sometimes for as long as three years. In addition, this slow adjustment may be attributable to social norms and notions of fairness that influence wage setting and that change only slowly over time.

To see what sticky nominal wages mean for aggregate supply, imagine that a firm has agreed in advance to pay its workers a certain nominal wage based on what it expected the price level to be. If the price level P falls below the level that was expected and the nominal wage remains stuck at W, then the real wage W/P rises above the level the firm planned to pay. Because wages are a large part of a firm's production costs, a higher real wage means that the firm's real costs have risen. The firm responds to these higher costs by hiring less labor and producing a smaller quantity of goods and services. In other words, because wages do not adjust immediately to the price level, a lower price level makes employment and production less profitable, which induces firms to reduce the quantity of goods and services supplied.

The Sticky-Price Theory Recently, some economists have advocated a third approach to the short-run aggregate-supply curve, called the sticky-price theory. As we just discussed, the sticky-wage theory emphasizes that nominal wages adjust slowly over time. The sticky-price theory emphasizes that the prices of some goods and services also adjust sluggishly in response to changing economic conditions. This slow adjustment of prices occurs in part because there are costs to adjusting prices, called menu costs. These menu costs include the cost of printing and distributing catalogs and the time required to change price tags. As a result of these costs, prices as well as wages may be sticky in the short run.

To see the implications of sticky prices for aggregate supply, suppose that each firm in the economy announces its prices in advance based on the economic conditions it expects to prevail. Then, after prices are announced, the economy experiences an unexpected contraction in the money supply, which (as we have learned) will reduce the overall price level in the long run. Although some firms reduce their prices immediately in response to changing economic conditions, other firms may not want to incur additional menu costs and, therefore, may temporarily lag behind. Because these lagging firms have prices that are too high, their sales decline. Declining sales, in turn, cause these firms to cut back on production and employment. In other words, because not all prices adjust instantly to changing conditions, an unexpected fall in the price level leaves some firms with higher-than-desired prices, and these higher-than-desired prices depress sales and induce firms to reduce the quantity of goods and services they produce.

Summary There are three alternative explanations for the upward slope of the short-run aggregate-supply curve: (1) misperceptions, (2) sticky wages, and (3) sticky prices. Economists debate which of these theories is correct. For our purposes in this book, however, the similarities of the theories are more important than the differences. All three theories suggest that output deviates from its natural rate when the price level deviates from the price level that people expected. We can express this mathematically as follows:

where a is a number that determines how much output responds to unexpected changes in the price level.

Notice that each of the three theories of short-run aggregate supply emphasizes a problem that is likely to be only temporary. Whether the upward slope of the aggregate-supply curve is attributable to misperceptions, sticky wages, or sticky prices, these conditions will not persist forever. Eventually, as people adjust their expectations, misperceptions are corrected, nominal wages adjust, and prices become unstuck. In other words, the expected and actual price levels are equal in the long run, and the aggregate-supply curve is vertical rather than upward sloping.

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