It is largely judgmental, based on trends in aggregate credit and sectoral credit growth in the macro-economic settings. For this reason, it has not been rule bound which will require either some model or at least some measurement of systemic risk and its sensitivity to the prudential parameters.
While the objective of the countercyclical policies is to increase the resilience of the system by building buffers to withstand shocks during downturns, the broader objective is to lean against the wind during the boom phase to dampen the credit and asset price boom. A more ambitious objective would be to ensure stable credit supply through the cycle-through booms and busts.