ECX5953 Economics
Open-Economy Macroeconomics
The Week 10 macroeconomics topic in ECX5953 Economics at Monash University opens the economy to trade and international lending: net exports (NX), net foreign investment (NFI), the identities S = I + NFI and NFI = NX = the current-account balance, the nominal and real exchange rate, and purchasing-power parity (PPP). It then traces how a government budget deficit, a tariff and capital flight move the real interest rate, the exchange rate and the trade balance. Get the two identities and the direction of each result right and these are among the most dependable structured-question marks in the final examination.
What this chapter covers
- 01Net exports NX = exports − imports (surplus if NX > 0, deficit if NX < 0)
- 02Net foreign investment NFI = domestic purchases of foreign assets − foreign purchases of domestic assets
- 03Core identity S = I + NFI: national saving funds home investment plus lending abroad (so NFI = S − I)
- 04Core identity NFI = NX = CAB: net lending abroad equals the trade balance equals the current-account balance
- 05The nominal exchange rate e; appreciation (e rises, stronger currency) vs depreciation (e falls)
- 06Real exchange rate = e × (P / P*); a real depreciation raises exports, cuts imports and lifts NX
- 07Purchasing-power parity (PPP): the law of one price implies e = P*/P; faster money growth depreciates the currency
- 08Budget deficit → national saving falls → r rises → NFI falls → currency appreciates → NX falls (the twin deficits)
- 09Tariff or import quota → currency appreciates but NX is UNCHANGED (it changes neither S nor I)
- 10Capital flight → NFI rises → domestic interest rate rises AND the currency depreciates
Real exchange rate and the PPP benchmark
- +1Price of the domestic basket expressed in US dollars = A$100 × 0.90 US$/A$ = US$90.
- +1Real exchange rate = e × P/P* = 0.90 × 100 / 75 = 90/75 = 1.20 — one Australian basket trades for 1.20 US baskets, so Australian goods are about 20% more expensive.
- +1PPP nominal rate = P*/P = 75/100 = 0.75 US$ per A$. The actual e = 0.90 is above 0.75, so the A$ is overvalued relative to PPP (consistent with the real rate exceeding 1).
- +1A real exchange rate above 1 makes exports dearer and imports cheaper, so it puts downward pressure on NX; a real depreciation (e falling toward 0.75, or domestic prices easing relative to foreign) would restore competitiveness and lift NX.
Key terms
- Net exports (NX)
- Exports minus imports — the trade balance. NX > 0 is a trade surplus, NX < 0 a trade deficit. In the open-economy model NX = NFI = the current-account balance.
- Net foreign investment (NFI)
- Domestic residents' purchases of foreign assets minus foreigners' purchases of domestic assets — the net flow of lending abroad. It equals national saving minus domestic investment, NFI = S − I.
- S = I + NFI
- The open-economy saving identity: national saving funds domestic investment plus net foreign investment. It follows from Y = C + I + G + NX with S = Y − C − G.
- Nominal exchange rate (e)
- The rate at which two currencies trade, here quoted as units of foreign currency per A$. A rise in e is an appreciation (stronger A$); a fall is a depreciation.
- Real exchange rate
- The rate at which the goods of one country trade for those of another: e × (P/P*). A value above 1 means domestic goods are relatively expensive; a real depreciation raises net exports.
- Purchasing-power parity (PPP)
- The long-run theory that a currency buys the same basket everywhere (the law of one price via arbitrage), implying a real exchange rate of 1 and a nominal rate e = P*/P.
- Twin deficits
- The result that a government budget deficit lowers national saving, raises the real interest rate, cuts NFI, appreciates the currency and so reduces net exports — a budget deficit accompanied by a trade deficit.
- Capital flight
- A sudden fall in demand for a country's assets (often from political or financial instability) that raises NFI, pushing up the domestic interest rate while depreciating the currency.
Open-Economy Macroeconomics FAQ
Is this Week 10 open-economy topic tested in the mid-semester test or the final exam?
The mid-semester test (20%; 45 multiple-choice questions, 90 minutes, one attempt) covers the Weeks 1–6 microeconomics block only, so the Week 10 open-economy material sits in the final examination (50% of the unit), held in the ~November 2026 Monash Semester-2 end-of-semester exam period. The exam's duration and open- or closed-book status are not stated in the unit materials, so confirm the exact date, duration and rules on Moodle.
Why does a tariff not reduce a trade deficit in this model?
Because the trade balance is set by saving and investment, not by trade policy. A tariff cuts imports at first, which raises demand for the currency and makes it appreciate, but it changes neither national saving S nor investment I. Since NFI = S − I is unchanged and NX = NFI, net exports are unchanged — exports and imports both fall by the same amount, so the appreciation offsets the initial import cut.
Can AI help me with open-economy macroeconomics in ECX5953?
Yes — Sia can explain the method step by step: how to derive S = I + NFI from the expenditure identity, compute a real exchange rate and a PPP benchmark, and trace the direction of each result for a budget deficit, a tariff or capital flight through the loanable-funds and foreign-currency markets. It is a study aid that walks you through the reasoning and checks your working; it does not sit your assessment for you or promise a particular grade, and it will not do work that must be your own.
Exam move
Anchor the whole chapter on the two identities and learn to derive them, not just recite them. Start from Y = C + I + G + NX, write national saving S = Y − C − G, and show that S = I + NFI with NFI = NX = the current-account balance; from there NFI = S − I is the workhorse for every numerical question. Next, drill the exchange-rate mechanics until they are automatic: distinguish the nominal rate from the real rate = e × (P/P*), and use PPP (e = P*/P) as the long-run benchmark, remembering that a real depreciation raises net exports. Finally, practise the three comparative-static traces through the loanable-funds and foreign-currency markets — a budget deficit (r up, NFI down, currency appreciates, NX down: the twin deficits), a tariff (currency appreciates but NX unchanged) and capital flight (r up and currency depreciates). Always finish with the one-sentence interpretation stating the correct direction of every arrow, because markers reward the signed chain, not just the final number.
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