  Sensitivity analysis is routinely performed on simplified surrogate models as
the cost of such analysis on the original model may be prohibitive. Little is
known in general about the induced bias on the sensitivity results. Within the
framework of chemical kinetics, we provide a full justification of the above
approach in the case of variance based methods provided the surrogate model
results from the original one through the thermodynamic limit. We also provide
illustrative numerical examples in context of a Michaelis--Menten system and a
biochemical reaction network describing a genetic oscillator.
