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In economics, aggregate supply is the total supply of goods and services that firms in a national economy plan on selling during a specific time period. It is the total amount of goods and services that firms are willing to sell at a given price level in an economy.
There are two main reasons why Qs might rise as P rises, i.e., why the AS curve is upward sloping:
- aggregate supply is usually inadequate to supply ample opportunity. Usually this is fixed capital equipment. The AS curve is drawn given some nominal variable, such as the nominal wage rate. In the short run, the nominal wage rate is taken as fixed. Thus, rising P implies higher profits that justify expansion of output. In the neoclassical long run, on the other hand, the nominal wage rate varies with economic conditions. (High unemployment leads to falling nominal wages -- and vice-versa.)
- An alternative model starts with the notion that any economy involves a large number of heterogeneous types of inputs, including both fixed capital equipment and labor. Both main types of inputs can be unemployed. The upward-sloping AS curve arises because (1) some nominal input prices are fixed in the short run (as in the neoclassical theory) and (2) as output rises, more and more production processes encounter bottlenecks. At low levels of demand, there are large numbers of production processes that do not use their fixed capital equipment fully. Thus, production can be increased without much in the way of diminishing returns and the average price level need not rise much (if at all) to justify increased production. The AS curve is flat. On the other hand, when demand is high, few production processes have unemployed fixed inputs. Thus, bottlenecks are general. Any increase in demand and production induces increases in prices. Thus, the AS curve is steep or vertical.
AS is targeted by government "supply side policies" which are meant to increase productivity efficiency and national output. For example, education and training and research and development.
There are generally three forms of aggregate supply (AS). They are:
- Short run aggregate supply — During the short-run, firms possess one fixed factor of production (usually capital). This does not however prevent outward shifts in the SRAS curve, which will result in increased output/real GDP at a given price. Therefore, a positive correlation between price level and output is shown by the SRAS curve.
- Long run aggregate supply (LRAS) — Over the long run, only capital, labour, and technology affect the LRAS in the macroeconomic model because at this point everything in the economy is assumed to be used optimally. In most situations, the LRAS is viewed as static because it shifts the slowest of the three. The LRAS is shown as perfectly vertical, reflecting economists' belief that changes in aggregate demand (AD) have an only temporary change on the economy's total output.
- Medium run aggregate supply (MRAS) — As an interim between SRAS and LRAS, the MRAS form slopes upward and reflects when capital as well as labor can change. More specifically, the Medium run aggregate supply is like this for three theoretical reasons, namely the Sticky-Wage Theory, the Sticky-Price Theory and the Misperception Theory. When graphing an aggregate supply and demand model, the MRAS is generally graphed after aggregate demand (AD), SRAS, and LRAS have been graphed, and then placed so that the equilibria occur at the same point. The MRAS curve is affected by capital, labor, technology, and wage rate.
In a standard aggregate supply demand model, the output (Y) is the x axis and price (P) is the y axis. An increase in aggregate demand shifts the AD curve rightward, bringing the equilibrium point horizontally along the SRAS until it reaches the new AD. This point is the short run equilibrium.
- Elmer G. Wiens: Classical & Keynesian AD-AS Model - An on-line, interactive model of the Canadian Economy.