Aggregate Income, Aggregate Consumption, and Aggregate Saving

The 1964 tax cut was not designed to influence consumption in isolation but rather to have an impact on the overall economy via its effect on consumption. So far, we have argued that a change in taxes leads to a change in disposable income and hence a change in consumption. Now we complete the story, noting that a change in consumption will itself affect the level of real GDP and hence have further effects on the level of disposable income. In the case of the Kennedy tax cut of 1964, the economists advising the administration at that time had a fairly specific idea of how changes in consumption would affect the overall economy. They argued that the $10 billion tax cut would lead to an increase in GDP of about $20 billion each year. How did they create this estimate? To answer this question, we need to embed our theory of consumption in the aggregate expenditure model. We motivated our consumption function by thinking about the behavior of an individual household. We now presume that our household is in some sense average, or representative of the entire economy, so the consumption relationship holds at an economy-wide level. Different households might actually have different consumption functions, but when we add them together, we still expect to find an aggregate relationship similar to the one we have described. The economists of the time used a framework that was closely based on the aggregate expenditure model. When prices are sticky, the level of GDP is determined in that model by the condition that planned spending and actual spending are equal. The model tells us that the level of real GDP depends on the level of autonomous spending and the multiplier, real GDP = multiplier × autonomous spending,

where the multiplier is calculated as ( 1

1 − marginal propensity to spend ). Given the level of autonomous spending

in the economy and given a value for the marginal propensity to spend, we can calculate the equilibrium level of real GDP. The marginal propensity to spend is not the same thing as the marginal propensity to consume, although they are connected. The marginal propensity to spend tells us how much total spending changes when GDP changes. Total spending includes not only consumption but also investment, government purchases, and net exports, so if any of these are responsive to changes in GDP, then the marginal propensity to spend is affected. Likewise, autonomous spending is not the same as autonomous consumption. Autonomous spending is the sum of autonomous consumption, autonomous investment, autonomous government purchases, and autonomous net exports. Finally, the marginal propensity to consume measures how consumption responds to changes in disposable income, not GDP. Toolkit: Section 16.19 “The Aggregate Expenditure Model” You can review the aggregate expenditure model and the multiplier in the toolkit.