  Thanks to the space-based photometry missions CoRoT and Kepler, we now
benefit from a wealth of seismic data for stars other than the sun. In the
future, K2, Tess and Plato will provide further observations. The quality of
this data may allow kernel-based linear structural inversion techniques to be
used for stars other than the sun. To understand the limitations of this
approach, we analyse the validity of the linear assumption used in these
inversion techniques. We inspect various structural pairs and see how they are
affected by structural changes. We show that uncertainties in radius strongly
affect structural pairs of nondimensional variables, and that various other
effects might come into play. Amongst these, the importance of micro-physics
give the most striking example of how uncertainties in stellar models impact
the verification of the linear relations. We also point out that including
seismic constraints in the forward modelling fit helps with satisfying the
linear relations.
