  The effects of isospin-symmetry breaking on the observables for
parity-violating electron scattering are investigated within the framework of
the nuclear shell model for 12C, 16O, and 28Si. Contributions due to mixing
with low-lying states as well as admixtures of 1p-1h configurations (via the
radial wave functions) are accounted for. It is found that isospin-mixing can
be important, and the consequences regarding precision tests of the standard
model are addressed.
