Investment and Economic Activity

Investment and Aggregate Demand

In the short run, changes in investment cause aggregate demand to change. Consider, for example, the impact of a reduction in the interest rate, given the investment demand curve (ID). In Figure 14.6 "A Change in Investment and Aggregate Demand", Panel (a), which uses the investment demand curve introduced in Figure 14.5 "The Investment Demand Curve", a reduction in the interest rate from 8% to 6% increases investment by $50 billion per year. Assume that the multiplier is 2. With an increase in investment of $50 billion per year and a multiplier of 2, the aggregate demand curve shifts to the right by $100 billion to AD₂ in Panel (b). The quantity of real GDP demanded at each price level thus increases. At a price level of 1.0, for example, the quantity of real GDP demanded rises from $8,000 billion to $8,100 billion per year.

Figure 14.6 A Change in Investment and Aggregate Demand

A reduction in the interest rate from 8% to 6% increases the level of investment by $50 billion per year in Panel (a). With a multiplier of 2, the aggregate demand curve shifts to the right by $100 billion in Panel (b). The total quantity of real GDP demanded increases at each price level. Here, for example, the quantity of real GDP demanded at a price level of 1.0 rises from $8,000 billion per year at point C to $8,100 billion per year at point D.

A reduction in investment would shift the aggregate demand curve to the left by an amount equal to the multiplier times the change in investment.

The relationship between investment and interest rates is one key to the effectiveness of monetary policy to the economy. When the Fed seeks to increase aggregate demand, it purchases bonds. That raises bond prices, reduces interest rates, and stimulates investment and aggregate demand as illustrated in Figure 14.6 "A Change in Investment and Aggregate Demand". When the Fed seeks to decrease aggregate demand, it sells bonds. That lowers bond prices, raises interest rates, and reduces investment and aggregate demand. The extent to which investment responds to a change in interest rates is a crucial factor in how effective monetary policy is.