  The aim of the present paper is to provide criteria for a central bank of how
to choose among different monetary-policy rules when caring about a number of
policy targets such as the output gap and expected inflation. Special attention
is given to the question if policy instruments are predetermined or only
forward looking. Using the new-Keynesian Phillips curve with a cost-push-shock
policy-transmission mechanism, the forward-looking case implies an extreme lack
of robustness and of credibility of stabilization policy. The backward-looking
case is such that the simple-rule parameters can be the solution of Ramsey
optimal policy under limited commitment. As a consequence, we suggest to model
explicitly the rational behavior of the policy maker with Ramsey optimal
policy, rather than to use simple rules with an ambiguous assumption leading to
policy advice that is neither robust nor credible.
