The nachral interest rate--some say neutral, Is the rate when the output gap is closed. It goes up when technology improves, And when population growth increases. In the very long run, those effects fade. They are long-run, not very-long-run shifts. Higher saving rates can make it go down. That shift persists in the very long run. For why, turn to the Solow Growth Model. And, given an open economy, Higher saving rates in other countries Can also lower the Na Chur All rate