Economic data — upon which we base our policy decisions — appear at different times and with different qualities: for instance, some economic series (such as trade and investment data) are subject to considerable revision over time.
Moreover, the transmission lags of monetary policy changes are often long, uncertain, and perhaps even contingent on the state of economy (for example whether it is an expansionary or contractionary phase). Last, but certainly not least, policy making itself does not operate in a vacuum or in a laboratory. There is the practical backdrop of legal, constitutional, cultural, and political economy constraints etc.