First, it implies that the economy’s usual rate of output growth, when employment is at its maximum and prices are stable, will be significantly slower than the post-World War II average. Slower economic growth, in turn, implies businesses will see less need to invest in expansion. And it implies families and individuals will feel the need to save more and spend less.
Because interest rates are the mechanism that brings the supply of savings and the demand for investment funds into balance, more saving and less investment imply a lower neutral interest rate. Although we can’t directly measure the neutral interest rate, it is something that can be estimated in retrospect.