In an open economy Y = C + I + G + NX, national saving (S) is defined as Y – C – G and therefore S = I + NX. Mathematically, if national saving (S) is greater than investment then net exports are greater than zero. Conceptually, the extra saving will flow out of the country, causing the real exchange rate to fall, and net exports to rise. In a small open economy, the interest rate is equal to the world interest rate.