This generally wasn’t necessary during the Great Moderation, when the economy was largely subject to a series of demand shocks. The inflation target could be achieved without causing undesirable volatility in 2  output and employment (so-called “divine coincidence” ). Despite the crisis, divine coincidence has continued to reign in the euro area and the US (see charts in the Appendix). Large output gaps and below-target inflation have pointed monetary policy in the same direction. That, unfortunately, has not been the case in the UK economy, which has been subject to a series of major supply shocks over the past five years, creating tensions between short-term output and inflation stabilisation. Brexit is the latest and potentially largest example. Brexit is a regime shift that has markedly increased the range of possible outcomes for the UK economy and therefore the potential paths of monetary policy. 1  Another dimension to uncertainty is ‘model’ uncertainty around the structure of the economy. That is distinct from uncertainty about possible future events, or ‘shocks’, affecting economy. Model uncertainty captures uncertainty around how the economy responds to those events, including to changes in monetary policy itself. 2 See Blanchard, O., and J. Galí (2007). "Real Wage Rigidities and the New Keynesian Model". Journal of Money, Credit, and Banking, 39(1), pp. 35-65.
Crucially, the Committee has also initiated an annual stock take of the supply side of the economy. It now publishes its best collective judgments on the natural rate of unemployment, the output gap, as well as the expected growth in productivity, labour supply and potential output. To draw out these points consider three examples of forward guidance by the MPC. The first occurred five years ago when the economy began to recover from the worst downturn since the Great Depression. During previous periods of accelerating growth and firming business confidence, the MPC had always tightened policy significantly (as evidenced in the correlation between survey indicators and MPC votes seen in Chart 1). On the basis of this past behaviour, the MPC would have raised interest rates by 2 to 3 percentage points between August 2013 and the end of 2014. For anyone who might suggest the MPC should have followed that reaction function, note that, even on unchanged policy, CPI inflation in the summer of 2016 was running at only about ½% and core CPI inflation around 1¼%. 3  In other words, the amount of volatility in interest rates should match the amount of uncertainty surrounding the economy. There should ideally be no additional volatility, or risk premium, due to uncertainty about how policy would respond.