A method is presented that accounts for the effects of singlet-triplet mixing in measured lifetimes of resonance and intercombination lines in alkaline-earthlike and inert-gaslike isoelectronic sequences. The method uses measured lifetimes and spectroscopic energy levels as its only inputs, and yields mixing-reduced line strength factors that can be isoelectronically linearized for precision interpolation, extrapolation, and smoothing. The method is applied to predictively systematize lifetimes in the Be, Mg and Ne iso-electronic sequences.