AD–AS model

The AD–AS or aggregate demand–aggregate supply model (also known as the aggregate supply–aggregate demand or AS–AD model) is a widely used macroeconomic model that explains short-run and long-run economic changes through the relationship of aggregate demand (AD) and aggregate supply (AS) in a diagram. It coexists in an older and static version depicting the two variables output and price level, and in a newer dynamic version showing output and inflation (i.e. the change in the price level over time, which is usually of more direct interest). The AD–AS model was invented around 1950 and became one of the primary simplified representations of macroeconomic issues toward the end of the 1970s when inflation became an important political issue. From around 2000 the modified version of a dynamic AD–AS model, incorporating contemporary monetary policy strategies focusing on inflation targeting and using the interest rate as a primary policy instrument, was developed, gradually superseding the traditional static model version in university-level economics textbooks. The dynamic AD–AS model can be viewed as a simplified version of the more advanced and complex dynamic stochastic general equilibrium (DSGE) models which are state-of-the-art models used by central banks and other organizations to analyze economic fluctuations. Unlike DSGE models, the dynamic AD–AS model does not provide a microeconomic foundation in the form of optimizing firms and households, but the macroeconomic relationships ultimately posited by the optimizing models are similar to those emerging from the modern-version AD–AS model. At the same time, the latter is much simpler and consequently more easily accessible for students, making it a widespread tool for teaching purposes.