Chapter 11 – The Aggregate Expenditures Model
2. A part of every increase in disposable income will not be spent but will be saved.
3. Test yourself with Quick Quiz 11.2.
V. Other Features of Equilibrium GDP
A. Savings equals planned investment.
1. It is important to note that in our analysis above we spoke of “planned” investment. At
GDP = $470 billion in Table 11.2, both saving and planned investment are $20 billion.
2. Saving represents a “leakage” from spending stream and causes C to be less than GDP.
3. Some of output is planned for business investment and not consumption, so this
investment spending can replace the leakage due to saving.
a. If aggregate spending is less than equilibrium GDP as it is in Table 11.2, line 8 when
GDP is $510 billion, then businesses will find themselves with unplanned inventory
investment on top of what was already planned. This unplanned portion is reflected
as a business expenditure, even though the business may not have desired it, because
the total output has a value that belongs to someone—either as a planned purchase or
as an unplanned inventory.
b. If aggregate expenditures exceed GDP, then there will be less inventory investment
than businesses planned as businesses sell more than they expected. This is reflected
as a negative amount of unplanned investment in inventory. For example, at $450
billion GDP, there will be $435 billion of consumer spending and $20 billion of
planned investment, so businesses must have experienced a $5 billion unplanned
decline in inventory because sales exceeded what they expected.
B. No unplanned changes in inventories.
1. Consider row 7 of Table 11.2 where GDP is $490 billion, here C + Ig is only $485 billion
and will be less than output by $5 billion. Firms retain the extra $5 billion as unplanned
inventory investment. Actual investment is $25 billion, or $5 billion more than the $20
billion planned. So $490 billion is an above-equilibrium output level.
2. Consider row 5, Table 11.2. Here $450 billion is a below-equilibrium output level
because actual investment will be $5 billion less than planned. Inventories decline below
what was planned. GDP will rise to $470 billion.
VI. Changes in Equilibrium GDP and the Multiplier
A. As developed in Chapter 10, an initial change in spending will be acted on by the multiplier
to produce larger changes in output.
1. The “initial change” represented in the text and Figure 11.3 is in planned investment
spending. It could also result from a nonincome-induced change in consumption.
2. The multiplier in Figure 11.3 is 4 (=1/MPS)
B. Figure 11.3 shows the impact of changes in investment. Suppose investment spending rises
(due to a rise in profit expectations or to a decline in interest rates).
1. Figure 11.3 shows the increase in aggregate expenditures from (C + Ig)0 to (C + Ig)1. In
this case, the $5 billion increase in investment leads to a $20 billion increase in
equilibrium GDP.
2. Conversely, a decline in investment spending of $5 billion is shown to create a decrease
in equilibrium GDP of $20 billion to $450 billion.
VII. International Trade and Equilibrium Output
A. Net exports (exports minus imports) affect aggregate expenditures in an open economy.
Exports expand and imports contract aggregate spending on domestic output.
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