A correlation technique has been developed to make the accuracy of complex and long-running resonance treatments available in fast, routine calculations. The technique is based on the subgroup method and is used to generate group-averaged resonance reaction rates. By fitting the correlation to several detailed auxiliary resonance calculations, a set of weights (the Lebesgue measure) is obtained. The weights can then be applied to a wider range of new cases. Use of the correlation technique results in one-tenth the computational burden of the detailed resonance treatment, yet the results duplicate the detailed calculations to within 0.01% in keff.