  Uncertainty quantification of complex technical systems is often based on a
computer model of the system. As all models such a computer model is always
wrong in the sense that it does not describe the reality perfectly. The purpose
of this article is to give a review of techniques which use observed values of
the technical systems in order to take into account the inadequacy of a
computer model in uncertainty quantification. The techniques reviewed in this
article are illustrated and compared by applying them to applications in
mechanical engineering.
