  In Quantum Physics there are circumstances where the direct measurement of
particular observables encounters diffculties; in some of these cases, however,
its value can be evaluated, i.e. it can be inferred by measuring another
observable characterized by perfect correlation with the observable of
interest. Though an evaluation is often interpreted as a measurement of the
evaluated observable, we prove that the two concepts cannot be identified in
Quantum Physics, because the identifcation yields contradictions. Then, we
establish the conceptual status of evaluations in Quantum Theory and the role
can be ascribed to them.
