It is implausible that the natural interest rate is so low that monetary policy would be ineffective. Does volatility in global financial markets render monetary policy ineffective? The volatility recently observed in global financial markets certainly makes it more difficult to clearly see the effects of the negative interest rate policy.
Immediately after the introduction of the negative interest rate policy, stock prices rose, with the Nikkei index adding 800 points in two days, while the yen fell to 121 yen against the U.S. dollar.