We need to know for example, if the central bank lowers interest rates below zero or engages in asset purchases, will that stimulate aggregate demand? Central banks have for the most part not engaged in these types of policy before so there is no (or very limited) historical correlation upon which we can fall back.
On the cost side, the same increase in the policy rate might cut output by up to 1 per cent and push inflation down by 0.5 percentage point relative to what it would have been otherwise.