Such an exercise is essentially identical to the common practice of constructing Taylor rules for monetary policy, as in Chart 2. Chart 4 draws the macro-prudential policy-implied path of US bank capital ratios. In deference to the architect of modern theories of credit-induced instability, let us call this the “Minsky rule” [Minsky, 1986]. The path of the Minsky rule is, in many respects, the mirrorimage of the Taylor rule. It suggests that hypothetical US banks’ capital ratios would have been systemically and significantly tighter than their actual path between 2000 and 2009. In  2  BIS central bankers’ speeches  other words, a tight macro-prudential stance would have counteracted the effects of a loose monetary policy stance. Although it is impossible to know for certain, it seems plausible that having this extra degree of policy freedom would have helped stabilise the US economy and financial system. A tighter bank capital regime would have tended to slow pre-crisis credit growth, thus constraining the boom. And more capital in the US banking system would have helped protect the wider economy from the credit crunch that followed the bust. In short, the boombust cycles in US credit and GDP would have plausibly been somewhat less severe had US policy been ambidextrous. The euro-zone crisis As a second historical example, consider the behaviour of some euro-zone crisis countries. In the run-up to monetary union, monetary policy was loosened significantly in a number of the peripheral European countries whose interest rates converged on core euro-area countries.
While a small step for mankind, this is a giant one for bank regulators. It is also, inevitably, something of a step into the unknown. What will be the impact of changes to the CCB on credit and growth? Will the two arms of policy (monetary and macroprudential) be better than one? And, if so, what institutional arrangements best deliver those benefits? Policy experience from the recent past and the present can shed light on these questions. The US dotcom bubble As a first case study, consider the behaviour of the US economy after the bursting of the dotcom bubble in 2001. Chart 2 plots US official interest rates in the period just before and after this event. Interest rates fell sharply, from 6.5% at the beginning of 2001 to 1% by the middle of 2003, to cushion the effects of the financial headwinds created by the dotcom bubble popping. Consider now what interest rate path would have been predicted had policy been responding mechanically to deviations of inflation from target and output from potential – in other words, following a standard “Taylor rule” [Taylor, 1993]. As Chart 2 shows, this would have implied a less dramatic fall in interest rates in the US. After the dotcom crash, a gap opened up between actual and Taylor-rule implied US interest rates. This was both sizable (on average, one or two percentage points) and persistent (lasting from early 2001 right up until summer 2008).