  The variances and covariances associated to the nuclear matrix elements (NME)
of neutrinoless double beta decay are estimated within the quasiparticle random
phase approximation (QRPA). It is shown that correlated NME uncertainties play
an important role in the comparison of neutrinoless double beta decay rates for
different nuclei, and that they are degenerate with the uncertainty in the
reconstructed Majorana neutrino mass.
