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In a private closed consumption expenditure and gross investment, expenditure generates aggregate expenditure. The aggregate expenditure model studies the relationship between aggregate expenditure and the output of an economy.

In the above graph, the aggregate expenditure increases as real domestic output increases. The aggregate expenditure makes equilibrium with the GDP as the AE curve intersects the 45Ëš line at the Y level of Real GDP.

When aggregate expenditure decreases, the AE curve shifts downward, making a new equilibrium with the real domestic output at Y’ level.

The fall in GDP is greater than the fall in aggregate expenditure due to the multiple effects initiated by initial reduced spending.

For example, a fall in consumption reduces the demand for goods, which reduces the demand for investment and thus leads to a reduction in investment expenditure as well. The effect increases further, and the fall in final GDP is higher than the initial fall in consumption spending.

It can be concluded from the above graph that a change in initial total spending induced a larger change in real GDP.

$k=\frac{∆realGDP}{∆initialspending}$

This is called the multiplier effect (k).