Estimation of inaccuracies in oscillator strength calculations

In recent years, the quality and resolution of observational data notably from the Hubble Space Telescope, has so improved that the accuracy of atomic data is frequently the limiting factor in progress. It is therefore imperative not merely that atomic data of improved accuracy are determined, but also that a realistic assessment of that accuracy is provided. Calculations of oscillator strengths are necessarily approximate. We discuss various indicators of accuracy, how semi-empirical corrections can be made to improve ab initio results, and how this data can be used to assess the level of accuracy of calculations for specific transitions. By way of illustration, these ideas are applied to set estimates of accuracy of a recent calculation of the lifetime of the 2s2p(3) S-5(2) degrees level of N II.