The following is from a Federal Reserve publication:
In practice, monetary policymakers do not have up-to-the-minute, reliable information about the state of the economy and prices. Information is limited because of lags in the publication of data. Also, policymakers have less-than-perfect understanding of the way the economy works, including the knowledge of when and to what extent policy actions will affect aggregate demand. The operation of the economy changes over time, and with it the response of the economy to policy measures. These limitations add to uncertainties in the policy process and make determining the appropriate setting of monetary policy ... more difficult.
If the Fed itself admits that there are many obstacles in the way of effective monetary policy, why does it still engage in active monetary policy rather than use a monetary growth rule, as suggested by Milton Friedman and his followers?