Economic Definition of marginal propensity to invest. Defined.
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Term marginal propensity to invest Definition: The proportion of each additional dollar of national income that is used for investment expenditures. Or alternatively, this is the change in investment expenditures due to a change in national income. Abbreviated MPI, the marginal propensity to invest is the slope of the investment line used in the analysis of Keynesian economics. As such, it also plays a role in the slope of the aggregate expenditure line and the multiplier effect.