Different diagnostics for the approximation quality of wavefunction methods are discussed: the weighted T-1 and D-1 norm, the deviation from the full configuration interaction wavefunction, and the variance of the trial wavefunction. All diagnostics are evaluated for the H-4 model system. Various wavefunction based approaches are analyzed. The wavefunction variance performs as a very reliable quantity to estimate the accuracy of the wavefunction and the energy expectation value. Although significantly more expensive than the evaluation of a plain energy expectation value the calculation of the wavefunction variance seems to be a comprehensive substitute for a full configuration interaction calculation. (C) 2008 Elsevier B. V. All rights reserved.