The Mundell–Fleming Model

Under perfect capital mobility, the domestic interest rate, after enduring a shock such as a monetary/fiscal expansion/contraction, returns to its original level eventually. In the SOE case, the original level of the interest rate is the world rate of interest. We know from the standard closed economy IS-LM analysis that a change in monetary policy shifts the LM curve while a change in fiscal policy shifts the IS curve. In an open economy, one policy change may shift both LM and IS curves. For example and under a flexible exchange rate regime, a monetary expansion has direct effect on the LM curve and shifts the LM curve towards the right initially; then the resulted increase in the exchange rate (depreciation) has the consequence of moving the IS curve to the right as well, a phenomenon similar to the effect of a fiscal expansion. Likewise and under a fixed exchange rate regime, a fiscal expansion has direct effect on the IS curve and shifts the curve towards the right initially. However, since the exchange rate is fixed, the deterioration in the current account may not be exactly offset by the amount of capital inflows, leading to an adjustment or change in official reserves and money supply. This consequently changes the LM curve position. From such preliminary reasoning, we become aware that, in an open economy, the economy may benefit from the implementation of a policy in more areas and to a larger extent than in a closed economy. The opposite is also true and the economy can be put in a state of complete mess.