Uncertainties due to Imperfect Knowledge of Systematic Effects: General Considerations and Approximate Formulae

Starting from considerations about meaning and subsequent use of asymmetricuncertainty intervals of experimental results, we review the issue ofuncertainty propagation. We show that, using a probabilistic approach (theso-called Bayesian approach), all sources of uncertainty can be included in alogically consistent way. Practical formulae for the first moments of theprobability distribution are derived up to second-order approximations.