Aggregate Spending Depends Positively on Income

The economy is in equilibrium when spending equals real GDP. We saw in Figure 10.7 “The Relationship between the Real Interest Rate and Spending on Durable Goods” that, as the real interest rate increases, the level of spending on durables decreases. This leads to a decrease in spending, given the level of income, and thus a decrease in the intercept of the spending line, as shown in Figure 10.9 “Increases in Real Interest Rates Reduce Real GDP”. The magnitude of the reduction in spending—that is, the shift downward in the spending line—will depend on the sensitivity of durable spending to real interest rates. The more sensitive durable spending is to changes in the real interest rate, the larger the shift in the spending line will be when the real interest rate changes.

As a consequence of increases in real interest rates, aggregate spending decreases. The initial reduction in spending induced by the increased real interest rate is then magnified by the multiplier process. The reduction in durable spending leads to a contraction in output. The resulting decrease in income leads households to spend less, leading to further contractions in output and income. In the end, the overall reduction in output exceeds the initial reduction in spending. This is visible in Figure 10.9 “Increases in Real Interest Rates Reduce Real GDP” from the fact that the horizontal difference between the old and new equilibrium points is larger than the vertical shift in the spending line. Toolkit: Section 16.19 “The Aggregate Expenditure Model” You can review the aggregate expenditure model and the multiplier in the toolkit. The Real Interest Rate–Real GDP Line We can summarize much of the monetary transmission mechanism by means of a relationship between real interest rates and real GDP, as shown in Figure 10.10 “The Relationship between the Real Interest Rate and Real GDP”. After we work through all the connections from real interest rates to the various components of spending and real GDP, we find that there is a level of real GDP associated with each real interest rate. The higher the interest rate, the lower is real GDP.