The evaluation of policy actions by means of macroeconomic models often begins with the analysis of multipliers. A rough analysis recommends to use those instruments that exhibit large multipliers. Government budget usually imposes some constraints on the policy action. Insted of the raw multiplier, a trade-off criterion could measure the effect of a variation of the instrument associated with a given cost in terms of government deficit. The trade-off criterion can be computed from the macroeconomic model, and this paper shows how to associate a standard error to the point estimate, thus providing a measurement of reliability of the policy instrument.